212Chapter11Quick Check 101. Why is imbibition considered the first step in seed germination?2. What might happen if nutrient mobilisation is disrupted during germination?3. How do temperature and light interact to regulate seed germination?11.4 GrowthTypes of Growth Curves: Absolute Growth Curve, Absolute Growth Rate Curve and Relative Growth Rate CurveTypes of Growth Curves1. Absolute growth curve(a) Represents the total increase in size or mass of an organism or structure over time.(b) Typically plotted as total biomass, length or volume on the y-axis against time on the x-axis.(c) Shows the overall trend of growth, often forming a sigmoid(S-shaped) curve in organisms exhibiting typical growth phases (such as lag, exponential and stationary phases).Mass / gABCTime / weeksFigure 11.24 Absolute growth curve. A is lag phase; B is log or exponential phase; C is decelerating or linear growth phase; D is stationary phase.2. Absolute growth rate curve(a) Shows the rate of increase in size or mass per unit of time.(b) Calculated as: Absolute Growth Rate = Final size – Initial sizeTime interval(c) When plotted, it usually forms a bell-shaped curve, with a peak during the exponential phase of growth.(d) Indicates periods of slow growth (lag phase), rapid growth (exponential phase) and declining growth (stationary phase).• Explain the types ofgrowth curves: absolutegrowth curve, absolutegrowth rate curve andrelative growth rate curve• Explain with examplesthe patterns of growth:limited growth in humans,unlimited growth inperennial plant, allometricgrowth in humans,isometric growth in fishand intermittent growth insect and crustacean• Explain the processesof ecdysis andmetamorphosis in insectsLearning OutcomeRemember the three types of growth curves and their shapes, using an organism as an example, like humans.Remember the formulae for absolute growth rate and relative growth rate.Exam TipsBiology Semester 2 STPM Chapter 11 Reproduction, Development and Growth
213ChapterRate of growth(increase inmass / g per week)Inflexion pointab cdTime / weeksFigure 11.25 Absolute growth rate curve. The curve is divided into four phases. The gradient at b shows the rate of increase, whereas that of c shows the rate of decrease. The peak indicates the maximum rate of growth. This is the inflexion point that marks the beginning of a decrease in rate before the adult size is reached.3. Relative growth rate curvePercentage increase in massa100b Figure 11.26 Four phases (a, b, c and d) are observed as in the graph of the relative growth rate curve. Note that phase “a” is a slow gain or “b” is a drastic drop, phase “c” is a gentle drop, whereas phase “d” is stationary. The highest point is generally found at the beginning of life.(a) The relative growth rate curve measures the growth rate relative to the initial size of the organism or structure. Relative Growth Rate = Change in sizeInitial size × Time(b) It is often plotted as percentage growth per unit time example of how to measure the change in size is to determine the change between the final measurement and the measurement.(c) The relative growth rate curve generally shows a declining trend because, as an organism increases in size, the relative contribution of new growth decreases over time.(d) Relative growth rate takes into consideration the existing sizeor mass of an organism. It is more meaningful than the absolute growth rate due to the amount of growth depends on the size or mass already present.Biology Semester 2 STPM Chapter 11 Reproduction, Development and Growth
(e) The curve is a measurement of the efficiency of growth. If the relative growth rate is high, its efficiency is proportionately high at that time. When the drop is steep, the drop in efficiency is big.Table 11.10 Type of growth curve. These growth curves are crucial in understanding the development of individual, agricultural productivity and ecological studies.Growth Curve Type Definition Graph Shape Key InsightsAbsolutegrowth curveTotal increase in size over timeSigmoid (S-shaped)Shows overall growth trendAbsolutegrowth rate curveRate of growth per unit timeBell-shaped Highlights peak growth phasesRelative growth rate curveGrowth rate relative to initial sizeDownwardslopingReflects decreasing relative growth as size increasesFactors Affecting the Pattern and Rate of Growth1. Growth in organisms is influenced by both internal and external factors, which determine the pattern (growth curve shape) and (speed) of growth. 2. These factors can be categorised into genetic, hormonal, nutritionaland environmental influences.Table 11.11 Factors that affect growth and factors is essential in agriculture, medicine, and conservation biology, as they help in improving crop yields, treating growth disorders and managing ecosystems efficiently.Factor Effect on Growth ExampleGenetic factors Determines maximum potential growthDifferent species have varying growth ratesHormonal factorsRegulates cell division, elongation and differentiationGH in humans; auxins in plantsNutritional factorsProvides raw materials for growth and metabolismProtein deficiencystunts growthEnvironmental factorsAffects metabolism, enzymeactivity and resource availabilityLow temperature slows down plant growthBiotic factors Competition, symbiosis and predation influence growthMycorrhizal fungi enhance root growthStress factors Can inhibit or slow growth Pollutants can reduce plant heightBiology Semester 2 STPM Chapter 11 Reproduction, Development and Growth
215ChapterPhases in the Sigmoid Growth Curves 1. Growth in an individual organism typically follows a sigmoid(S-shaped) curve, known as the logistic growth curve. 2. This curve consists of distinct phases that reflect changes in the growth rate over time. 3. The key phases are:(a) Lag phase• Characterised by slow growth as the organism adjusts to its environment.• Cells or tissues are metabolically active but undergoingminimal cell division.• Involves adaptation processes, such as enzyme activation nutrient uptake.• Example: A newly germinated seed takes time to acenzymes and absorb water before rapid cell division begins.(b) Exponential (Log) phase• The fastest growth phase, where cell division occurs at a constant and rapid rate.• High metabolic activity and efficient nutrient utilisationsupport maximum growth.• Growth follows an exponential pattern, where size or mass doubles at regular intervals.• Example: Human infants show rapid height and wincrease in early childhood.(c) Decelerating phase• Growth rate begins to slow down due to increasing competition for nutrients and space.• Cells or tissues still grow, but at a reduced rate.• Hormonal changes may influence differentiation over proliferation.• Example: In humans, growth slows after puberty as resourcesshift toward maintenance rather than a rapid increase in (d) Stationary (Plateau) phase• Growth reaches a steady state, with little or no net increase in size.• Occurs when cell division equals cell death or when an organism reaches its final mature size.• Energy is nowused for maintenance, repair and reproductionrather than growth.• Example: A fully mature adult human maintains body but does not grow taller.(e) Senescence and decline phase (in some cases)• Some organisms exhibit a declining phase, where tissues degenerate due to ageing.Biology Semester 2 STPM Chapter 11 Reproduction, Development and Growth
• Cellular damage accumulates, leading to reduced physiological efficiency.• Growth may become negative as body mass decreases.• Example: In old age, human height may decrease slightly to spinal compression, and muscle mass may decrease.4. A sigmoid (S-shaped) growth curve represents these phases when plotted as size or mass against time.5. There are alternative growth curves besides the S-shaped curve, namely J-shaped curve (exponential growth curve).(a) Seen in certain organisms, like bacteria in an unlimitedenvironment.(b) Growth remains exponential without a stationary phase, leading to a population crash when resources are exhausted.Patterns of Growth: Allometric Growth, Isometric Growth, Limited Growth, Unlimited Growth and Intermittent GrowthDifferent Growth Patterns of OrganismsOrganisms exhibit various growth patterns depending on their genetic makeup, environmental conditions and physiological adaptations. Th main types of growth patterns are:1. Allometric growth(a) Allometric growth parts of an organism, leading to changes in shape or proportionas the organism develops. (b) Different growth rates for different organs are observed throughout the life span of humans, where different tissues or organs grow at different speeds relative to each other, leading to changes in body proportions over time.(c) Since growth occurs at different rates in different parts of the organism, this leads to changes in shape and proportiontime.(d) Some body parts grow faster or slower than others.(e) It is controlled by differential gene expression and hormonal regulation.(f) Example:• Human body growth: The head is large in infants but grows proportionally smaller compared to the rest of the body as they mature.• Crabs: Claw size grows disproportionately larger compared to the rest of the body.Biology Semester 2 STPM Chapter 11 Reproduction, Development and Growth
217ChapterSize attained as percentage of total growth0 5 10 15150Lymhoid tissueFinal size of organTime from birth / years20010050Head Relative growthcurve of humanas a wholeReproductiveorgansFigure 11.27 Allometric growth curve in humans2 months(foetus)5 months(foetus)Newborn 2 years 6 years 12 years 21 years This image depicts development in humans, whereby the proportions of body parts change as an individual develops from a foetus to an adult. At birth, a human baby is not a miniature many of itssystems immature, but its overall morphology (form and shape) is also quite different than that of an adult. One significant difference is the ratio of head to trunk size. A baby’s head is much larger in comparison with the rest of its body than an adult’s head is, and the head stops growing much earlier in life than the rest of the body.2. Isometric growthThe external structure of fishretains its shape as a result ofan equivalent growth rate.Figure 11.29 Isometric growth curve (such as fish)Biology Semester 2 STPM Chapter 11 Reproduction, Development and Growth
(a) In an isometric growth curve, all body parts grow at the samerate, maintaining the same proportions throughout development.(b) The shape of the organism remains unchanged as it grows.(c) The curve occurs when cell division is uniform across tissues.(d) Example:• Fish and amphibians: Juveniles resemble miniature adults in shape, just at a smaller size.• Starfish: The body proportions remain the same as they grow.3. Intermittent growth(a) Intermittent growth occurs in discontinuous spurts, with periods of rapid growth followed by short periods of little or no growth when the organism is young.(b) Common in organisms that undergo moulting or metamorphosis.(c) Example:• Insects (such as grasshoppers, crabs and lobsters): Growth occurs after moulting (ecdysis) when the old exoskeleton newly shed and the new exoskeleton is still soft, followed period of hardening. • Amphibians (such as frogs): Growth is rapid during tadpole stages and slows after metamorphosis into adults.Length / gTime / daysinstar5thinstarFigure 11.30 Intermittent growth curve in arthropods4. Limited growth(a) Growth slows down and eventually stops after reaching mature size.(b) Follows a sigmoid (S-shaped) growth curve, with phases:• Lag phase (slow growth)• Exponential phase (rapid growth)• Stationary phase (growth stops, maintenance begins)(c) Common in most animals and higher plants.(d) Example:• Mammals, birds and reptiles: Growth stops after reachingadulthood.• Trees: Some stop growing in height after maturity but continue increasing in girth.Biology Semester 2 STPM Chapter 11 Reproduction, Development and Growth
219ChapterMass / kg0 5 10 15 20 2550Time / years80706040302010ConceptionBirthInstant growth spurtChildhood growthAdolescentgrowth spurtFigure 11.31 Limited growth curve5. Unlimited growth(a) Growth continues throughout the organism’s lifetime without a definite stopping point.(b) Follows a J-shaped growth curve in ideal conditions where resources are unlimited.(c) Occurs in organisms with indeterminate growth, such as many plants and simple animals. • Fish and some reptiles (such as crocodiles and turtles) grow continuously throughout life.• Trees(such as coconut palm) grow taller and widerindefinitelyunder favourable conditions.Time / yearsDriedweight / kgFigure 11.32 Unlimited growth curvePrimary and Secondary Growth in Plants1. Plant growth occurs through two main types:(a) Primary growth – Increases plant length(b) Secondary growth – Increases plant girth (thickness)Biology Semester 2 STPM Chapter 11 Reproduction, Development and Growth
2202. Primary growth(a) Definition:• Growth that increases the length of roots and shoots.• Occurs in all plants, including monocots and dicots.(b) Location:• Takes place at the apical meristems (root and shoot tips).• Apical meristems contain actively dividing cells that elongate the plant.(c) Process:• Cell division → Cell elongation → Cell differentiation• Leads to the formation of primary tissues such as:➢ Epidermis (protective layer)➢ Cortex (storage and support)➢ Vascular tissues (xylem & phloem) for transport(d) Example:• Root and shoot tips of herbaceous plants, grasses and youngtrees.3. Secondary Growth(a) Definition:• Growth that increases the thickness of stems and roots.• Occurs in woody plants and dicots, but is absent in monocots.(b) Location:• Takes place in lateral meristems:➢ Vascular cambium – Produces secondary xylem (wand secondary phloem.➢ Cork cambium – Forms rotective outer ayer (c) Process:• Vascular cambium produces new xylem (inside) and phloem (outside).• Cork cambium produces cork cells, forming bark.• Growth rings (annual rings) form due to seasonal variationsin xylem production.(d) Example:• Woody trees, shrubs and gymnosperms (such as oak, pine).Table 11.12 Comparison of primary growth and secondary growthFeature Primary Growth Secondary GrowthFunction Increases length Increases thicknessLocation Apical meristems Lateral meristemsTissues producedPrimary xylem, phloem, epidermisSecondary xylem (wood), phloem, corkOccurs in All plants (monocots &dicots)Dicots and gymnosperms (not in monocots)Example Root and shoot elongation in herbsWood formation in trees• Primary growth allows plants to grow taller and reach sunlight.• Secondary growthstrengthens woody plants and enables long-term survival.• Both types of growth work together to support plant functionand survival.Biology Semester 2 STPM Chapter 11 Reproduction, Development and Growth
221ChapterDormancy in Life1. Dormancy is a temporary state in which an organism reduces its metabolic activity, growth and development to survive unfavourable environmental conditions. 2. It is a crucial adaptation seen in plants, animals and microorganisms to conserve energy and resources during periods of stress.3. Types of dormancy(a) Dormancy in plantsPlants enter dormancy to survive adverse conditions like cold winters or dry seasons.• Seed dormancy➢ A condition where seeds remain inactive even favourable conditions.➢ Prevents germination until optimal environmental cues are met.➢ Due to hard seed coat, immature embryo, chemical inhibitors and light or temperature dependence.• Bud dormancy➢ Many trees stop growing in winter to avoid frost damage.➢ Regulated by hormones (abscisic acid promotes dormancy, gibberellins break dormancy).• Underground organ dormancy➢ Bulbs, tubers and rhizomes remain dormant in seasons.➢ xample: Potato tubers remain inactive until conditions are favourable.(b) Dormancy in Animals Animals enter dormancy to conserve energy during extenvironmental conditions.• Hibernation (Winter dormancy)➢ A deep sleep-like state in cold environments to conserve energy.➢ Metabolism, heart rate and breathing slow down.➢ Example: Bears, ground squirrels and bats hibernate winter.• Aestivation (Summer dormancy)➢ A state of dormancy during hot and dry conditionsprevent desiccation.➢ Common in desert and amphibious animals.➢ Example: African lungfish buries itself in mud, snails their shells and frogs hide underground.• Diapause➢ A pause in development in insects to survive seasonalchanges.➢ Example: Mosquito larvae stop developing in winter and resume in spring.Biology Semester 2 STPM Chapter 11 Reproduction, Development and Growth
222Processes of Ecdysis and Metamorphosis in InsectsArthropods, including insects, crustaceans and arachnids, undergo e(moulting) and metamorphosis as part of their growth and development.Ecdysis and Metamorphosis in Arthropods1. Ecdysis (Moulting)(a) Definition:Ecdysis is the shedding of the exoskeleton to allow growth in arthropods. Since the exoskeleton is rigid and non-expandable, arthropods must periodically moult and form a new, larger exoskeleton.TemperatureCerebralganglionNeurosecretionThoracicglandReleased incorpus cardiacumEcdyson Juvenile hormoneEpidermis EpidermisAdult skin Juvenile skinFood Figure 11.33 Ecdysis regulation (b) Process of ecdysis:Ecdysis occurs in several stages:• Pre-moult (Apolysis)➢ The old exoskeleton separates from the underlying epidermis.➢ Epidermal cells secrete enzymes that digest the inner layers of the old cuticle.Quick Check 111. In what scenarios is the relative growth rate curve more useful than the absolute growth curve?2. How does the growth mechanism in arthropods affect their adaptability to environmental changes compared to molluscs?Biology Semester 2 STPM Chapter 11 Reproduction, Development and Growth
223Chapter• Secretion of new cuticle➢ The epidermis secretes a new soft cuticle under the old exoskeleton.• Shedding of old exoskeleton (Moulting)➢ The old cuticle splits open, and the arthropod crawls out.➢ This stage is controlled by the ecdysone hormone(moulting hormone).• Post-moult (Hardening of new exoskeleton)➢ The new cuticle expands and hardens through sclerotisation (cross-linking of proteins).➢ Calcium deposition occurs in crustaceans to strengthen the exoskeleton.(c) Significance of ecdysis:• Allows growth by replacing the restrictive exoskeleton.• Essential for metamorphosis and development in insects.• Occurs multiple times during an arthropod’s life cycle.2. Metamorphosis(a) Definition:Metamorphosis is the biological process of transformation in arthropods, involving distinct changes in body form, structureand physiology from immature stages to adulthood.(b) Types of metamorphosis:• Complete metamorphosis (Holometabolism)➢ Involves four distinct stages: Egg → Larva → Pupa → Adult.➢ Seen in mosquitoes, butterflies, beetles, flies and bees.AdultEggsLarvaPupaEcdyson + juvenile hormone EcdysonEgg First Second Third Fourth Fifth Pupa ImagoInstar larval stagesFigure 11.34 Control of insect hormones in complete metamorphosisMetamorphosisVIDEOBiology Semester 2 STPM Chapter 11 Reproduction, Development and Growth
➢ Stages:➩ Egg – Fertilised egg develops into a larva.➩ Larva – A worm-like feeding stage (such as caterpillarsin butterflies).➩ Pupa (Chrysalis) – A dormant stage where restructuring occurs.➩ Adult – The fully developed reproductive stage.➢ Significance:➩ Larvae and adults do not compete for food.➩ Specialised body forms allow efficient adaptationdifferent environments.• Incomplete metamorphosis (Hemimetabolism)➢ Involves three stages: Egg → Nymph → Adult➢ Seen in grasshoppers, cockroaches, termites and dragonflies.AdultEggsHatching4th moult5th moultmoultInstar 1ststage nymphInstar 2nd stage nymphInstar 4thstage nymphInstar 5thstage nymphEcdyson + juvenile hormone Ecdyson First Second Third Fourth Fifth Instar nymphal stagesFigure 11.35 Control of insect hormones in incomplete metamorphosis➢ Stages:➩ Egg – Fertilised egg hatches into a nymph.➩ Nymph – Resembles the adult but lacks wingsreproductive structures.➩ Adult – Fully developed with functional wings reproductive organs.Biology Semester 2 STPM Chapter 11 Reproduction, Development and Growth
225Chapter➢ Significance:➩ Nymphs and adults share similar habitats and food.➩ Development is gradual, without a pupal stage.Table 11.13 Comparison of ecdysis and metamorphosisFeature Ecdysis (Moulting) MetamorphosisDefinition Shedding of the exoskeleton to growTransformation from immature to adult formControlled by Ecdysone hormone Juvenile hormone (JH) and ecdysoneOccurs in All arthropods Mainly in insectsProcess type A physical process A developmental processStages Multiple moults in the life cycleDistinct life cycle stages (complete / incomplete)Roles of Hormones in Ecdysis and Metamorphosis1. In arthropods, ecdysis (moulting) and metamorphosis are regulated by a complex hormonal system. The three key hormones involved are:(a) Prothoracicotropic hormone (PTTH) – Stimulates ecdysonesecretion.(b) Ecdysone (moulting hormone) – Controls ecdysis.(c) Juvenile hormone (JH) – Determines ofmetamorphosis.2. Ecdysis (moulting) hormonal regulation Ecdysis allows arthropods to shed their exoskeleton and grow. The process is controlled by:(a) Prothoracicotropic hormone (PTTH)• Secreted by the brain (neurosecretory cells).• Stimulates the prothoracic gland to release ecdysone.(b) Ecdysone (moulting hormone)• A steroid hormone produced by the prothoracic gland.• Triggers the synthesis of new cuticle and initiates moulting.• High levels of ecdysone lead to the separation of the old exoskeleton (apolysis).3. Metamorphosis hormonal regulation Metamorphosis involves transformation from larva → pupa → adultin holometabolous insects or nymph → adult in hemimetabolous insects. The process is controlled by:(a) Juvenile hormone (JH)• Secreted by the corpora allata (endocrine gland in the brain).• Ecdysis is essential for growth and survival, while metamorphosisenables arthropods to undergo majordevelopmentaltransformations.• These adaptations help arthropods colonisediverse habitats and reduce competition between life stages.Exam TipsRemember! Brain hormone (secreted by neurosecretory cells), juvenile hormone (secreted by corpora allata) and ecdysone (secreted by prothoracic glands) are key regulators of insect development and metamorphosis. Neurosecretory cells, located in the brain, release brain hormone / prothoracicotropic hormone (PTTH), which stimulates the prothoracic glands to produce ecdysone, the moulting hormone. Juvenile hormone regulates larval growth and prevents metamorphosis, while ecdysone initiates moulting and metamorphosis when JH levels are low.Exam TipsBiology Semester 2 STPM Chapter 11 Reproduction, Development and Growth
• High JH levels: Prevent metamorphosis, maintaining the larval stage.• Low JH levels: Allow transformation to the pupal stage.• Absence of JH: Allow adult formation.(b) Ecdysone and JH Interaction• Larval moult → High JH + Ecdysone → New larva forms.• Pupal moult → Low JH + Ecdysone → Pupa forms.• Adult moult → No JH + Ecdysone → Adult emerges.BrainPTTHEcdysoneEarly larva Laterlarva PupaAdultProthoracicglandLow JHJuvenilehormone(JH)Neurosecretory cellsCorpus cardiacumCorpus allatumFigure 11.36 Hormonal regulation of insect development. In insects, moulting and development are controlled by a combination of hormones:• A brain hormone stimulates the release of ecdysone from the prothoracicgland. • Juvenile hormone promotes the retention of larval characteristics.• Ecdysone promotes moulting (in the presence of juvenile hormone) development (in the absence of juvenile hormone) of adult characteristics.Table 11.14 Hormonal Control in InsectsHormone Function Secreted byPTTH Stimulates ecdysone productionBrain(neurosecretory cells)Thoracic glandstimulating hormoneStimulate the thoracic gland to produce ecdysoneCorpus cardiaca (singular: corpus cardiacum)Ecdysone Initiates moulting and growth Prothoracic glands (simulated by PTTH) Juvenile hormone (JH)Controls metamorphosis by maintaining larval characteristics, ensure a young exoskeleton is retainedCorpora allata (singular: corpus allatum)Biology Semester 2 STPM Chapter 11 Reproduction, Development and Growth
227Chapter4. Importance of JH and ecdysone Juvenile hormone (JH) and ecdysone are two key hormones that regulate growth, moulting (ecdysis) and metamorphosis in insects. Their interaction determines whether an insect remains in the larval/ nymph stage, transitions into a pupa, or develops into an adult.(a) Importance of juvenile hormone (JH)• Prevents premature metamorphosis➢ JH maintains larval characteristics, preventing transformation into the pupal or adult stage.➢ When JH levels are high, ecdysis produces a larger larva instead of a pupa or adult.• Regulates the type of moult➢ High JH + Ecdysone → Larva moults into another larval stage.➢ Low JH + Ecdysone → Larva moults into a pupa.➢ No JH + Ecdysone → Pupa moults into an adult.• Controls reproduction in adults➢ In adult insects, JH stimulates ovary development and egg production.➢ Example: In mosquitoes, JH regulates egg-laying behaviour.• Maintains the caste system in social insects➢ In bees, ants, and termites, JH determines whether an individual becomes a worker, soldier or reproductive queen.(b) Importance of ecdysone (moulting hormone)• Triggers moulting (ecdysis)➢ Ecdysone stimulates the breakdown of the old exoskeleton and formation of a new cuticle.➢ Essential for insect growth and size increase.• Initiates metamorphosis➢ Works in opposition to JH to control developmental transitions.➢ High ecdysone + low JH → Induces pupal formation.➢ High ecdysone + no JH → Leads to adult emergence.• Regulates tissue specialisation➢ In the pupal stage, ecdysone activates cell death and tissue specialisation, forming adult structures (for example, wings in butterflies).What happens if an insect cannot moult?If an insect cannot moult, it cannot grow. Without shedding its old exoskeleton, the new one becomes too tight, restricting movement and growth, ultimately leading to death.Exam TipsBiology Semester 2 STPM Chapter 11 Reproduction, Development and Growth
228Chapter11Table 11.15 Interaction between JH and ecdysoneHormone High JH + High Ecdysone Low JH + High Ecdysone No JH + High EcdysoneEffect on DevelopmentLarval moult (growth) Pupae moult (metamorphosis starts)Adult moult (final stage)Example Caterpillar growing into a larger caterpillarCaterpillar forming a pupa Butterfly emerging fthe pupaQuick Check 121. Why is metamorphosis considered an evolutionary advantage in insects?1. Spermatogenesis occurs in the seminiferous tubules of the testes, producing haploid sperm cells from diploid spermatogonia via mitosis and meiosis.2. Oogenesis occurs in the ovaries, forming mature ova from oogonia through meiotic division and follicle development.3. During ejaculation, sperm travels from the epididymis through the vas deferens, then to the urethra, and is deposited in the vagina, passing through the cervix, uterus and reaching the oviduct (fallopian tube) where fertilisation occurs.4. Fertilisation involves the fusion of a sperm and an ovum to form a diploid zygote in the oviduct. The zygote undergoes cleavage and forms a blastocyst, which travels to the uterus and implantsinto the endometrial lining for further development.5. Hormones in menstrual cycle, pregnancy and parturition(a) The menstrual cycle is regulated by FSH, LH, oestrogen and progesterone.(b) During pregnancy, hCG maintains the corpus luteum, while progesterone and oestrogen sustain the endometrium.(c) Parturition is triggered by oxytocin and prostaglandins, stimulating uterine contractions and cervical dilation.5. Significance in pest control and insect growth regulation(a) Synthetic JH for pest control• Synthetic JH mimics (such as methoprene) can be used insect growth regulators (IGRs).• Prevents larvae from maturing, controlling mosquitopopulations.(b) Ecdysone inhibitors as insecticides• Compounds that block ecdysone production can dimoulting and kill agricultural pests.Biology Semester 2 STPM Chapter 11 Reproduction, Development and Growth
229Chapter6. Three stages in human embryonic development(a) Cleavage is a rapid mitotic division of the zygote, forming a multicellular blastula.(b) Gastrulation reorganises the blastula into a three-layered embryo (ectoderm, mesoderm, endoderm).(c) Organogenesis is the formation of organs from the three germ layers, such as neural tube formation from the ectoderm.7. The placenta facilitates gas exchange, nutrient transfer, and waste removal between maternal and foetal blood. It also secretes hormones like hCG, progesterone and oestrogen to maintain pregnancy.8. Double fertilisation occurs in angiosperms, where one male gamete fuses with the egg to form a diploid zygote, and another gamete fuses with the two polar nuclei to form a triploid endosperm, which nourishes the developing embryo.9. After fertilisation, the zygote develops into an embryo with radicle, plumule, and cotyledons. The ovule becomes the seed, and the ovary wall develops into the fruit, aiding in seed protection and dispersal.10. Tissue culture and grafting in asexual reproduction(a) Tissue culture involves growing plant cells or tissues in nutrient media under sterile conditions to produce clones.(b) Grafting joins tissues of two different plants so they grow as one; commonly used in fruit and ornamental plants for desired traits.11. Imbibition is the initial uptake of water by dry seeds, causing them to swell and activate metabolic processes necessary for germination.12. Following imbibition, stored food in the endosperm or cotyledons is hydrolysed by enzymes like amylase into sugars and amino acids, which are transported to the growing embryonic axis for cell division and elongation.13. Germination requires appropriate water, oxygen and temperature. Some seeds may also require light or scarification to break dormancy.14. Types of growth curves(a) Absolute growth curve shows the total increase in size or mass over time.(b) Absolute growth rate curve indicates the rate of growth at a specific time.(c) Relative growth rate curve compares the growth rate per unit of initial size.15. Patterns of growth(a) Limited growth in humans: growth ceases after maturity.(b) Unlimited growth in perennial plants: continues throughout life.(c) Allometric growth in humans: body parts grow at different rates (for example, head versus limbs).(d) Isometric growth in fish: all parts grow at the same rate.(e) Intermittent growth in insects and crustaceans: occurs in steps due to moulting.16. Ecdysis (moulting) is the periodic shedding of the exoskeleton to allow growth in insects.17. Metamorphosis is the developmental transformation from larva to adult, which may be complete (such as a butterfly) or incomplete (such as a grasshopper).Biology Semester 2 STPM Chapter 11 Reproduction, Development and Growth
230Chapter11Objective Questions1. The acrosome of a sperm cell contains enzymes to digest which structure of the ovum?A Zona pellucidaB Corona radiataC Vitelline membraneD Receptor protein2. During which stage of embryonic development does implantation occur?A Morula C GastrulaB Blastocyst D Zygote3. Which of the following best describes the role of progesterone during pregnancy?A Induces ovulationB Triggers the LH surgeC Stimulates FSH releaseD Inhibits uterine contractions4. Which of the following comparisons between oestrogen and progesterone is correct?Oestrogen ProgesteroneA Secreted by Corpus luteum PlacentaB Function Maintains pregnancyInduces ovulationC Feedback on LHPositive NegativeD Effect on uterusThickens endometriumMaintains endometrium5. A woman has low progesterone levels ndexperiences repeated miscarriages in early pregnancy. What could be a possible reason?A Low progesterone leads to failure in endometrial maintenance B High oestrogen stimulates uterine contractionsC Low LH prevents embryo implantationD Excess FSH stimulates multiple ovulations6. Arrange the following events in the coorder for fertilisation and implantation:I Acrosomal reaction occurs.II Sperm binds to the zona pellucida.III Sperm nucleus fuses with the ovum.IV The blastocyst implants into the endometrium.V The cortical reaction prevents polyspermy.A I → II → III → V → IVB II → I → V → III → IVC II → I → III → V → IVD I → II → V → III → IV7. During lactation, hormone P stimulates the development of the breast lobule, hormone Q stimulates the production of milk in the breast lobule and hormone R controls the release of milk from the mammary gland. What are the hormones P, Q and R?P Q A Oxytocin Prolactin OxytocinB Progesterone Oxytocin ProlactinC Prolactin Progesterone OxytocinD Progesterone Prolactin Oxytocin8. Neurulation is the formation of the nerve cord. Which of the following is correct?A It is part of cleavage and originated from the ectoderm.B It is part of gastrulation and originated from mesoderm.C It is part of organogenesis and originated from ectoderm.D It is part of organogenesis and originated from endoderm.STPM PRACTICE 11Biology Semester 2 STPM Chapter 11 Reproduction, Development and Growth
231Chapter9. The diagram below shows a cross-section of a mammalian blastocyst. What happens to X and Y after implantation?YXBlastocyst cavity(blastocoele)EndometriumWall of uterusIt develops into .A X = amnion Y = chorionB X = chorion Y = embryonic C X = trophoblast Y = inner cell mD X = chorion Y = inner cell m10. Arrange the following events in correct order for pollen development in angiosperms:I Microspore mother cell undergoes meiosis.II Microspores undergo mitosis to form pollen grains.III Pollen grains mature into male gametophytes.IV Pollen sacs in the anther undergo differentiation.V Each pollen grain develops into a two-celled structure (vegetative and generative cells).A IV → I → II → V → IIIB I → IV → II → V → IIIC IV → II → I → V → IIID I → IV → V → II → III11. Which of the following correctly describes the sequence of events during germination in the cereal seed?I Water uptake activates the embryo.II Gibberellins are secreted by the embryo.III Aleurone layer produces hydrolyticenzymes.IV Starch in the endosperm is converted to maltose.V The radicle emerges, followed by the plumule.A II → I → IV → III → VB I → II → III → IV → VC III → I → II → IV → VD I → III → II → IV → V12. Which is true of the cells found in the anther and carpel of the hibiscus flower?Diploid HaploidA Pollen grains, embryo sac and fused polarnucleiPollen mother cells, embryo sacmother cells, male and femalegametesB Pollen grains, embryo sac, male and female gametesPollen mother cells, embryo sacmother and fused polar-nucleiC Pollen grains, embryo sac, male and female gametesPollen grains, embryo sac and fused polar-nucleiD Pollen mother cells, embryo sacmother and fused polar-nucleiPollen grains, embryo sac, male and female gametes13. The diagram shows the processes in seed germination.PSQ R Which of the following is not a function of P in this diagram during germination?Biology Semester 2 STPM Chapter 11 Reproduction, Development and Growth
232Chapter11A Synthesising amylase to break down stored starchB Producing proteases to hydrolyse storage proteinsC Secreting gibberellins to stimulate seedling growthD Releasing enzymes to mobilise nutrients for the embryo14. Which of the following is not a feature of isometric growth?A Body parts grow at the same te,maintaining proportion.B No change occurs in the shape of the organism as it grows.C Some body parts grow faster than others, leading to disproportionate features.D A fish that grows larger withoutchanging body proportions exhibits isometric growth.15. Which of the following best explains why insects exhibit intermittent growth?A Their exoskeleton restricts continuous growth, requiring moulting for size increase.B They undergo isometric growth, leading to proportional body expansion.C They follow a sigmoid growth curve with a prolonged lag phase.D Their body proportions remain unchanged throughout development.16. A researcher observes that a tree continuesto increase in girth and height throughout its lifetime, whereas a dog stops growing after reaching adulthood. What is the ostlikely explanation?A The tree follows intermittent growth, while the dog follows limited growth.B The tree exhibits unlimited growth, while the dog undergoes limited growth.C The dog undergoes isometric growth, while the tree undergoes allometric growth.D Both the tree and the dog exhibit same growth pattern, but at different rates.17. Which of the following correctly describes the role of ecdysone in insect development?I It is secreted by the prothoracic gland.II It stimulates the epidermis to initiate moulting.III It prevents metamorphosis when present in high amounts.IV It promotes the secretion of juvenile hormone (JH).A I and IIB II and IIIC III and IVD I and IV18. Which of the following is not a function of juvenile hormone (JH)?A Maintaining larval characteristics during moultingB Preventing the secretion of ecdysoneC Regulating the transition from larva to pupaD Ensuring proper timing of metamorphosis19. Arrange the following steps in the coorder for insect ecdysis (moulting):I PTTH is released from the brain.II The prothoracic gland secretes ecdysone.III Ecdysone triggers epidermal cell division and new cuticle formation.IV The old exoskeleton is shed.V The new exoskeleton hardens.A I → II → III → IV → VB II → III → I → IV → VC III → I → II → IV → VD I → III → II → V → IVBiology Semester 2 STPM Chapter 11 Reproduction, Development and Growth
233Chapter20. The graph represents the relative growth patterns of different human organs over time.Percentage of relative growth0 5 10 15 Time / years20015010050Final size of organIIIIIIIV Which human organs are represented by I, II, III and IV?General body growth (such as muscles, bones, viscera)Lymphoid system (such as thymus, lymph nodes, tonsils, spleen)Neural growth (such as brain, spinal cord, head circumference, eyes, skull size)Reproductive system (such as ovaries, testes, uterus, external genitalia, prostate glands, mammary glands)A III IV I IIB I III II IVC I II III IVD II I III IVStructure Questions1. Reproduction is regulated by a series of different hormones. The graph below shows changes in levels of female reproductive hormones A – D during a single menstrual cycle.A1 14Days7 21 28B C D(a) Identify hormones A and D in the graph. [2](b) Explain the significance of the sharp rise in hormone A around day 14. [2](c) Describe the role of hormone C after ovulation. [2](d) A common treatment for fertility problems is in vitro fertilisation (IVF). During IVF, awoman will be given medication containing hormone B. Explain why medication containingB is administered during IVF. [2]Biology Semester 2 STPM Chapter 11 Reproduction, Development and Growth
234Chapter11e Quiz 42. The hormonal control of metamorphosis in a butterfly is shown in the diagram below. BrainRLow level ofhormone QHormone QP(a) Identify the structures labelled P and R. [2](b) Name hormone Q and describe its role in insect development. [2](c) Explain how a low level of hormone Q and the product of R influence the morphological characteristics of the insect. [1](d) What is the function of structure R in the regulation of insect moulting? [1](e) Scientists can artificially regulate the levels of hormone Q in insects. How could this be applied in pest control? [1]Essay Questions1. (a) Explain how oral contraceptive pills prevent pregnancy by influencing reproductive hormones. [7](b) Describe the stages of embryonic development in dicot plants, including the heart-shaped and torpedo-shaped stages. [6]2. (a) Explain the hormonal regulation of human parturition. [8](b) Describe the growth pattern for fish and crab. [5]Biology Semester 2 STPM Chapter 11 Reproduction, Development and Growth
350Biology Semester 2 STPM Model Paper (964/2)Section A [20 marks]Answer all questions in this section.4. Which of the following statements is not true of Bohr’s effect?A Low PO2 in highly respiring tissue causes faster dissociation of oxyhaemoglobin.B Formation of haemoglobinic acid causes faster dissociation of oxyhaemoglobin.C Carbonic acid dissociates to form bicarbonate ions and proton ions.D Four molecules of O2 dissociated from oxyhaemoglobin. 5. The embryo of a dicotyledonous seed is shown in the diagram below.X Which statement is not true of A X and Y ensure a sufficient supply of nutrients to the embryo.B X withers during seed development.C Y is derived from the mitotic division of the apical cell.D Y aids in nutrient uptake from X.6. The diagram below shows a section through part of a seminiferous tubule. Which structure undergoes meiosis II?Leydig cellABC DSTPM MODEL PAPER (964 � 2)1. Which of the following causes the left shift of the oxygen dissociation curve (ODC)?A AnaemiaB ExerciseC Smaller body sizeD First day hiking in the Alps2. The diagram below shows a section of an alveolus. Cell PCapillaryendotheliumAlveolar spaceCell QRed blood cells Match the following functions to cells Q.I Secrete pulmonary surfactantII Engulf invaded pathogenIII Facilitate diffusion of substancesCell P Cell QA I IIB I IIIC II IIID III I3. Which of the following statements does not explain the mechanism of the opening of stomata in drought?A Proton pumps are inhibited.B Influx of Ca2+ ions into the guard cells.C Influx of K+ ions into the guard cells.D Water potential increases in the guard cells.
354Biology Semester 2 STPM Model Paper (964/2)Section B [14 marks]Answer all questions in this section.21. The diagram shows a foetus in the placenta.UterusChorionic villusXYZMembrane Q(a) Name blood vessel Y. [1 (b) State the function of Y. [1 [1 (d) State the structure that mainly protects the foetus if the blood group of the foetus and mother is incompatible.[1 (e) Describe how the structure named in 21(d) plays the relevant role.[1 (f) Describe the peak of oestrogen released by the placenta in the late third trimester of pregnancy.[2 marks
356Biology Semester 2 STPM Model Paper (964/2)Section C [26 marks]Answer all questions.23. (a) Fugu, the pufferfish, is one of the most renowned cuisines, and it needs qualified fugu handlers to remove the poison tetrodotoxin before serving. Consuming fugu contaminated with tetrodotoxin is lethal as the neurotoxin binds to sodium ion channels.Explain the mechanism of tetrodotoxin that leads to death. [6 marks(b) Explain how a horticulturist can correct accidental far-red light exposure to induce flowering in a named long-day plant?[7 marks24. (a) Explain how cyclosporine suppresses the immune response of the donor to minimise the risk of rejection of the grafted cells. [6 marks(b) Explain how economic growth plays a role in combating hand-foot-and-mouth disease (HFMD) in Malaysia?[7 marks
ANSWERS357Chapter8 Gaseous Exchange11. The upper respiratory tract primarily prepares air for entry into the lungs by filtering and conditioning it, whereas the lower respiratory tract is specialised for the exchange of oxygen and carbon dioxide, with alveoli playing a critical role.2. The alveoli have a large surface area, thin walls, and are surrounded by capillaries, which allows for rapid diffusion of oxygen and carbon dioxide due to the short distance and high surface area.3. The trachea and bronchi are lined with ciliated epithelium and mucus-secreting cells, which trap and expel foreign particles and pathogens, thus protecting the lungs from infection and irritation.21. Haemoglobin helps transport carbon dioxide from tissues to the lungs. It binds to carbon dioxide to form carbaminohaemoglobin or facilitates its conversion to bicarbonate ions.2. The partial pressure gradients drive the diffusion of oxygen from areas of high partial pressure (lungs) to low (tissues) and carbon dioxide from high (tissues) to low (lungs), facilitating efficient gas exchange.3. The enzyme carbonic anhydrase catalyses the conversion of carbon dioxide and water into carbonic acid, which dissociates into bicarbonate ions and hydrogen ions.31. The sigmoidal shape is due to cooperative binding, where the binding of one oxygen molecule to haemoglobin increases its affinity for additional oxygen molecules.2. The Bohr effect ensures that oxygen is released more readily in tissues with high carbon dioxide levels or low pH, such as actively respiring muscles, where it is most needed.3. The Bohr effect causes the oxygen dissociation curve to shift to the right, indicating a lower affinity of haemoglobin for oxygen under acidic or high carbon dioxide conditions.4. In COPD, the altered gas exchange and chronic hypoxia may affect the normal functioning of the Bohr effect, potentially leading to inadequate oxygen delivery to tissues during exertion.41. Breathing is controlled by the respiratory centres in the medulla oblongata and pons of the brainstem. These centres regulate the rate and depth of breathing based on signals from chemoreceptors and stretch receptors.2. Chemoreceptors in the carotid bodies and aortic bodies detect changes in blood levels of carbon dioxide, oxygen, and pH. Increased carbon dioxide or decreased pH stimulates the respiratory centres to increase breathing rate.3. Stretch receptors in the lungs prevent over-inflation by sending inhibitory signals to the respiratory centres, triggering exhalation (Hering-Breuer reflex).51. A spirogram is a graphical representation of lung volumes and capacities measured during breathing using a spirometer.2. Tidal Volume (TV): The amount of air inhaled or exhaled during normal breathing. Inspiratory Reserve Volume (IRV): The additional air inhaled after a normal inhalation. Expiratory Reserve Volume (ERV): The additional air exhaled after a normal exhalation. Residual Volume (RV): The air remaining in the lungs after maximal exhalation.3. Vital Capacity (VC): TV + IRV + ERV.Total Lung Capacity (TLC): VC + RV.Functional Residual Capacity (FRC): ERV + RV.Inspiratory Capacity (IC): TV + IRV.61. Stomata are primarily found on the lower epidermis of leaves in most plants, though some plants have stomata on both surfaces or only on the upper surface.2. The guard cells control the opening and closing of the stomatal pore, regulating gas exchange and water loss. Their thick inner walls and thin outer walls facilitate changes in shape during opening and closing. Chloroplasts in guard cells enable photosynthesis, which drives the mechanism of stomatal movement.71. Stomatal opening is triggered by light, low carbon dioxide levels, and water availability. Guard cells
AagglutinationClumping of bacteria or viruses together to form a bigger aggregatealdosteroneInvolves in homeostatic control of sodium ion in the bloodantibodyGlobular glycoprotein that acts against a particular antigenantigenA protein in which the body recognizes as foreign or non-selfBB cellsLymphocytes that mature in the bone marrow and then spread throughout the body. CSequence of events which makes up one heartbeat which consists of one systole and one diastolechemoreceptorsReceptor cells that can be stimulated by chemicalscholeraInfection in the small intestine caused by the bacterium Vibrio choleraDdeaminationconversion of an amino acid to a keto acid by the removal of the amine functional groupdengueAn infectious disease transmitted by a vector, Aedes aegypti mosquitodiastoleThe event that occurs when the heart muscle relaxes.double fertilisationA process in the flowering plant life cycle in which there are two fertilisations; one fertilisation results in the formation of zygote, whereas the second results in the formation of endosperm.EepitopeA small specific part of a larger antigen, which is capable to bind with a specific antibody.GgluconeogenesisSynthesis of glucose from non-carbohydrate sources such as lactate, glycerol, fatty acids and some amino acids.glycogenesisFormation of glycogen from glucose. This process is under the control of insulin.glycogenolysisBreakdown of glycogen to glucose to provide immediate energy and to maintain blood glucose levels.HhaemoglobinA respiratory pigment found in red blood cells to transport oxygen from lungs to the tissueshalophytesPlants that can live in soil with more than 0.5% of salt.hand-mouth-and-foot diseaseAn infection caused by enterovirus and coxsackievirus, transmitted via direct contact and airborne. Iincubation periodA period of time between exposure and onset of symptomsinfectious agentsBiological agents or pathogens that cause diseaseGLOSSARY
Purchaseebook here!W.M: RM40.95 / E.M: RM42.95AAEVSB2675031A2ISBN: 978-629-498-778-4Strategic STPM Biology Semester 2 is written based on the purified STPM Examination Syllabus by the Malaysian Examinations Council (MEC) and will be implemented starting from STPM Semester 1 in 2026. This book is carefully designed and well-organised, containing the following features to enhance students’ understanding of the concepts being studied.Strategic STPM Pre-U Text Titles:› Pengajian Am Semester 2 › Bahasa Melayu Semester 2 › Biology Semester 2 › Physics Semester 2 › Chemistry Semester 2 › Mathematics Semester 2 › Sejarah Semester 2 › Geografi Semester 2 › Ekonomi Semester 2 › Pengajian Perniagaan Semester 2Also available:› MUET My Way BIOLOGYPre-U TextStrategicSTPMSEMESTER2REVISION★ Comprehensive Notes★ Learning Outcomes★ Concept Maps★ SummariesREINFORCEMENT & ASSESSMENT★ Quick Checks★ STPM Practices★ STPM Model Paper Semester 2★ AnswersEXTRA FEATURES ★ Examples★ Exam Tips★ Digital Resources QR CODEFEATURES