CELL STRUCTURE AND ORGANELLES

BASIC UNDERSTANDING OF BIOLOGY FOUNDATION SEM 1: DB014

CHAPTER 2: CELL STRUCTURES AND FUNCTIONS

2.1 CELL AS UNIT OF LIFE

(a) Structures of prokaryotic and eukaryotic cells

(i) PROKARYOTIC CELL

FIGURE 1: Typical structure of prokaryotes (e.g. Bacteria)

1. Pro means before, karyon means nucleus. Eg: Bacteria and Archaea

2. Unicellular organisms without nucleus/ no distinct nucleus.
 Genetic material is circular DNA that is not enclosed in nuclear membrane. DNA is lying free

in the cytoplasm in a region called nucleoid.
 DNA is not associated with histone protein.
3. Diameter is small: 0.5 – 10.0µm

4. No membrane bound organelles. The only organelle is 70s ribosome for protein synthesis.

5. Other details structure of bacteria:

Structure Description and Function

Cell May folded to form mesosomes which store the enzymes that responsible for
membrane production of ATP.
Regulates movement of materials into and out of the cell.
Cell wall Composed of peptidoglycan.
Protects the cell and gives shape,.
Capsule Polysaccharide or protein coating secreted outside the cell wall for additional
protection.
Plasmid Protects the cell against some antibiotics and avoid from drying out.
Flagella Extra small circular DNA contains genes separated with main DNA.
Pili Propel in helical orientation for movement of bacterial cell.
Fimbriae Attach to each other or attach to the surfaces
Sex pilus is used to exchange genetic material during sexual reproduction/
conjugation.

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(ii) EUKARYOTIC CELL

1. Eu means true/ with, karyon means nucleus. Eg: Plants, animals, protists, fungi.

2. Make up of unicellular and multicellular organisms. The cells of eukaryotes show the present of

distinct nucleus.
 DNA is linear and enclosed within nuclear membrane
 DNA is associated with histone protein.
3. Large in size: 10 – 100µm
4. Have membrane bound organelles. Ribosomes are large, 80S as site for protein synthesis.

FIGURE 2: Eukaryotic cell

Compare the structure of prokaryotic and eukaryotic cell (plants and animal cells)

Similarities between prokaryotic and eukaryotic cell:
- Both cells contain DNA that carries genetic material.
- Both cells have ribosome that importance in protein synthesis.
- Both cells are bounded by a plasma membrane.
- Both cells have cytoplasm.

Differences between prokaryotic and eukaryotic cell:

Prokaryotes Eukaryotes
No distinct nucleus. DNA is lying free in the Has a distinct nucleus. DNA is enclosed in
cytoplasm. nuclear membrane.
DNA is circular and not associated with DNA is linear and associated with histone
histone protein protein
Do not have membrane bound organelles Have membrane bound organelles
Size of cell is generally smaller (0.5 – 10.0µm) Size of cell is generally larger(10 – 100µm)
Smaller ribosome, 70S Larger ribosome, 80S
Cell wall is made from peptidoglycan Cell wall is made from cellulose (plant cell)
and chitin (fungi)
Always unicellular Often multicellular
Simple flagella without 9+2 microtubule Complex flagella with 9+2 microtubule
arrangement arrangement
Cell division by binary fission without spindle Cell division by mitosis or meiosis.
formation, no mitosis nor meiosis Spindle is form.

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(b) Describe how cells are grouped into tissues and organ

FIGURE 3: Relation between cell, tissues, organ, system and organism
2.2 STRUCTURES AND FUNCTIONS: PLASMA MEMBRANE AND ORGANELLES
(a) Details structures of typical animal and plant cell

FIGURE 4: Detail structure of plant cell
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FIGURE 5: Detail structure of animal cell

Differences between plant and animal cell:

Animal cell Plant cell
No cell wall Have (rigid) cellulose cell wall.
No plasmodesmata Plasmodesmata found in the cell wall
No chloroplast Chloroplast present in photosynthetic cells
Small (temporary) vacuole Large, permanent central vacuole filled with sap
cell (comprise of mineral ions and waste products)
No tonoplast Tonoplast surrounds vacuole
Nucleus often central Nucleus usually peripheral in mature cell
Centrioles present No centrioles
Carbohydrate storage in the form of glycogen Carbohydrate storage in the form of starch
Some cells have cilia or flagella or microvilli No cilia and microvilli. Flagella in some specialized
cell/ lower plant male gamete/ sperm
Lysosomes present Lysosomes usually absent

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(b) Structure and functions of organelles

Nucleus

Structure:
 Nuclear envelope - a double membrane that enclose

nucleus (inner and outer membrane) that separates the

nuclear contents from the surrounding cytoplasm.
 Nuclear pores - control the movement of substances

into and out from the nucleus.(RNA, protein)
 Nucleoplasm - fluid in the interior part of nucleus

containing chromatin
 Nucleolus - one or two rounded and darkly area of

chromatin, involved in making rRNA for the synthesis

of ribosome.
 When the cell is not dividing, DNA exists as thin

elongated chromatins thread. Before cell division,

chromatin condenses to form thicker structure called

chromosome.

Function:
 Carry or store genetic material because it contains

DNA, the heredity materials.
 Control the activities of the cell

Mitochondria

Structure:
 Surrounded by a double membrane
 Outer membrane is smooth and permeable.
 Inner membrane is highly folded into cristae, which give

it a large surface area for the attachment of enzyme/

protein.
 Inner membrane divides mitochondria into two internal

compartment: intermembrane space and matrix of

mitochondria
 Mitochondrial matrix is the fluid- filled space that

contain its own DNA , ribosome and enzyme.

Function:
 Site of aerobic cellular respiration to produce energy

in the form of ATP.
 Krebs cycle – in matrix
 Electron transport chain – in inner membrane/ cristae

Chloroplast

Structure:
 Double membrane (inner and outer membrane)

organelles
 Lens shape organelle found in leaves or green part of

plant and algae
 Fluid-filled space inside the chloroplast is stroma.

Stroma contain enzymes, DNA and ribosomes
 Chloroplast contains disc-liked sacs called thylakoid.
 Thylakoid arrange in stacks called granum. The

arrangement of thylakoid increases the surface area for

attachment of photosynthetic pigments (chlorophyll and

carotenoids). (Singular - granum; Plural - grana)

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Function:
 Site of photosynthesis.

 Light dependent reaction - at thylakoid membrane
 Light independent reaction - in stroma

* Both mitochondria and chloroplast are semiautonomous organelles which are
able to replicate freely.

Endoplasmic reticulum (ER)
 ER form extensive network of interconnecting tubules or

sacs called cisternae with internal space called lumen.
 Continuous with nuclear envelope.

Structure Function

Rough Series of 1) Site of temporary

ER interconnected storage of protein.

flattened sac. 2) Intracellular

Ribosome attach on transports protein.

the outer surface

which give it its

rough appearance.

Smooth Consist of 1) Synthesis and

ER interconnected transport of lipids.

tubules. 2) Detoxification of

Lack of ribosome drug/poison.
which give smooth 3) Storage of Ca2+.

appearance. 4) Carbohydrate

metabolism.

Golgi body

Structure:
 A stack of flattened membranous sacs called

cisternae with lumen
 The sacs are not physically connected
 Cis face (entry face) facing the rough ER to receives

transport vesicles from ER.
 Trans face (exit face) facing the plasma membrane.

New vesicles bud off and transported out from Golgi

body to other site of cell.

Function:
 Received, modified, packaged, sorted and transport

protein, carbohydrates and lipid from ER to other

parts of the cell.
 Produce lysosome
 Produce polysaccharides for the cell wall formation in

plant

Lysosomes

Structure:
 Found in animal cell. It is a membranous sac of

hydrolytic enzymes use to digest macromolecule that

work best in acidic environment.

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Function:
 Intracellular digestion/phagocytosis: to digest food

particles or bacteria
 Autophagy (recycle own organic material/ digest

excess or worn out organelles)
 Autolysis (digestion of entire cell)

Centrioles

Structure:
 Centrioles consist of a pair of short microtubules.

Both are at right angle of each other.
 Each centriole made up of 9 triplets of microtubule

arrange in the ring.
 Microtubule is long and hollow rods made from

tubulin protein.
 Centrosome is a region where a pair of centrioles

located. It is a region where the microtubules grow out

to form spindle fiber during cell division (also called

microtubule-organizing center).

Function:
 Involved in cell division (animal cell) - initiate the

spindle that organizes and separates the chromosomes.

Ribosome

Structure:
 Composed of protein and rRNA, in two subunit (large

and small)
 Ribosome are not membrane bounded.
 Manufactured in the nucleolus of the nucleus.
 Some found freely in groups called polyribosomes and

some attached to the surface of endoplasmic reticulum
 Cell that has high rate of protein synthesis have large

number of ribosome.

Function:
 The sites of protein synthesis.
 Ribosomes on rough ER synthesized protein for the

plasma membrane or secrete outside cell
 Free ribosomes synthesized protein used in cytoplasm.

Endomembrane system

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 Endomembrane system is a collection of membranous structures involved in transport within

the cell.
 They are interacting through direct connection by vesicles. The main components of the

endomembrane system are:

- Nuclear envelope
- Endoplasmic reticulum
- Golgi apparatus
- Lysosome, vesicles and vacuoles
- Plasma membrane

(c) Structure of plasma membrane based on Fluid Mosaic Model

FIGURE 6: Structure of plasma membrane based on Fluid Mosaic Model

Fluid Mosaic - Fluid because the phospholipid can move laterally or flip-flop and protein can
Model move laterally within the phospholipid bilayer
(by S.J Singer
& Nicolson) - Mosaic because the various protein is embedded in or attach to phospholipid
bilayer give mosaic appearance

(d) Structure of plasma membrane and the function of its components

Component Explanation
Phospholipids - Cell membrane consists of phospholipid bilayer with various protein molecules

embedded in or attached to it.
- A phospholipid is an amphipathic molecule, meaning it has both hydrophobic and

hydrophilic regions.
- The (polar) hydrophilic head of phospholipid points outwards and attracted to

the water / aqueous surrounding.
- The (non-polar) hydrophobic tail of phospholipid faces inwards to each other
- Function: Phospholipids make the cell membrane selectively permeable.
- It prevents hydrophilic (ionic and polar molecules) molecules from diffusing

across the membrane, but allows the diffusion of hydrophobic molecules.

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Proteins - Phospholipid bilayer has various protein molecules embedded in or attach to it.
(i) There are peripheral proteins located on the outer and inner surfaces of the
*peripheral = membrane. It loosely bounded to the surface of the plasma membrane.
extrinsic (ii) The integral proteins are fully embedded or partially embedded in the
membrane. It tightly bound to the phospholipid bilayer. Integral proteins that
* integral = penetrate fully through the membrane are called transmembrane protein that
intrinsic can act as transport protein (carrier or channel protein).

- Functions of protein:
1. Act as transport protein (carrier or channel protein).
2. Involve in enzymatic activity.
3. Signal transduction
4. Cell-cell recognition
5. Intercellular joining
6. Attachment to cytoskeleton and extracellular matrix.

Carbohydrate - Usually branched oligosaccharides chain
chain - Carbohydrate chain attach to phospholipid is called glycolipid
- Carbohydrate chain attach to protein is called glycoprotein
Cholesterol - Oligosaccharides are varying from individual to individual.
- Function: cell-cell recognition or act as cell marker.

- Cholesterol are found between phospholipid bilayer of animal cell only
- Function: Cholesterol regulate the fluidity of the membrane at different

temperature/ increases flexibility and stability of membrane
- At warm temperatures, it makes the membrane more rigid by restrains the

movement of phospholipids and reduces fluidity.
- At cool temperatures, it maintains fluidity by preventing tight packing of

phospholipids.

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2.3 CELLS ARE GROUPED INTO TISSUES
(a) Describe animal tissues and plant tissues

ANIMAL TISSUE

Epithelial tissue Nervous tissue Muscle tissue Connective tissue
Forms the external surfaces Sense stimuli and Composed of fibres/ Bind and support
of the body, cover the outer transmit signals in the cells that are capable of other tissues in the
and inner surfaces of organs form of nerve impulses contraction to produce
and some are specialized to from one part to movement in the body body

form glandular tissues another

**Simple squamous **Motor neuron **Smooth muscle **Blood
epithelium Skeletal muscle
Sensory neuron Cardiac muscle Hyaline
**Simple cuboidal cartilage
epithelium Interneuron Compact bone
neuron
**Simple columnar
epithelium

PLANT TISSUE

Meristematic tissue **Ground tissue Permanent tissue
Cells that capable undergo 1. parenchyma Mature cell which
2. collenchyma incapable cell division
cell division 3. sclerenchyma
**Vascular tissue
**apical meristem

lateral meristem

Intercalary meristem Xylem Phloem
** Type of tissue that is cover in DB014 syllabus 1. vessel element 1. sieve tube
2. tracheid 2. companion cell

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(b) State type, structure, function and distribution of animal and plant tissues

i. Animals cells and tissues -epithelial tissue
General characteristics of epithelial tissue

(a) Cells at the base are attached to a thin sheet of connective tissue called basement membrane.

(b) Cells are tightly/ closely packed together, with almost no intercellular spaces.

(c) Cells do not supply with blood vessels.

i. Simple squamous epithelium

Structure: Location: Function:
 Cells are flat and thin Lining of alveoli of lung, Regulates movement of
Lining of blood vessel, substances/ exchange of
 Disc-shaped nucleus at the

centre Lining of part of kidney, material by diffusion.

lining of mouth cavity

ii. Simple cuboidal epithelium

Structure: Location: Function:
 Cells are cuboid in shape (all Lining of kidney tubules Absorption and secretion.

side same length) and lining of ducts and

 Large spherical nucleus at the glands (E.g: salivary gland)

centre

iii. Simple columnar epithelium

Structure: Ciliated (with cilia at the Function:
 To move substances
 Cells are elongated/ column like surfaces)  Filtering foreign particles

 Round to oval nucleus located - Location: Lining of *Cilia =hair-like structures at
the surface of cells
near the base uterus and fallopian tube,
 Relatively large cytoplasmic Lining of bronchioles of Function:
Absorption
volume. respiratory tracts
 Most are associated with goblet *Microvilli= tiny projections of
the plasma membrane that
cell, that is cell that secrete Non-ciliated (with increase the surface area of the
cell.
mucus as lubricant/ trap dust microvilli at the surfaces)
 Some simple columnar have - Location: Lining of

cilia or microvilli on the surface digestive tract (stomach,

intestine), part of kidney

tubule

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EPITHELIAL TISSUE

FIGURE 7: Simple squamous epithelium

FIGURE 8: Simple cuboidal epithelium

FIGURE 9: Simple ciliated columnar epithelium
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NERVE CELL (NEURON)

FIGURE 10: Structure of motor neuron

Types of neuron and its function

(i) Sensory/afferent Neurons -Transmit impulse from the receptor to the central nervous system(CNS)
(ii) Interneurons - Integrate impulse between sensory neuron and motor neuron.
(iii) Motor/ efferent Neurons - Transmit impulse from the central nervous system (CNS) to effectors

Details structure of motor neuron

Structure Function

B: Dendrites Receiving impulse and transmit it

- Highly branches cytoplasmic towards cell body

extension at the cell body

C: Cell body Nucleus controls all the activity of
- Contain nucleus and organelles the neuron
Conduct impulse away from cell
E: Axon body.
- long projection of neuron
- its plasma membrane is axolemma Speed up the impulse transmission
- some are covered by myelin sheath (because myelin sheath provides
electrical insulation)
F: Nodes of Ranvier
- gap between myelin sheath where Send impulse to another neuron or
effector.
impulse can jump to next node of
Ranvier

G: Synaptic knob/ terminal
- swollen ending of neurons, also

known as axon terminal
- Contain lot of mitochondria and

vesicles containing neurotransmitter.

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MUSCLE TISSUE Smooth muscle
Diagram

Spindle shape
with tapering
ends

Location Wall of digestive tract, urinary bladder, uterus, blood vessel (vein and arteries
Function wall)

Involuntary action such as propel food through gastrointestinal tract.(peristalsis)

Shape Spindle shape with tapering ends
Lack of striation (light and dark bands are absent).
Striations Has only one central nucleus per muscle cell

No of nuclei per Unbranched
fiber No
Branching

Present of
intercalated disc

CONNECTIVE TISSUES

Characteristic connective tissue
Consist of living cells with large amounts of ground substance or matrix

i. BLOOD
 Connective tissue with fluid matrix called blood plasma
 Plasma consist of water, proteins, salts and a variety of soluble chemical messengers such as hormone

that is transport from one part of the body to another

FIGURE 11: Components of the blood

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a. Erythrocytes (RBC) Types of blood cell c. Platelets
Structure : Structure
 Without nucleus to b. Leukocytes (WBC)  Also called

provide more space Structure thrombocytes
for hemoglobin  Contains nucleus.  have no nuclei
storage  Have 5 major type : monocytes, lymphocytes,  originate as
 Biconcave disc shape
to increase surface basophils, neutrophils and eosinophils pinched - off
area for effective  Shape is irregular or ammeboid cytoplasmic
gaseous exchange fragments of
 Has elastic Function large cells in
membrane to change  function in defense system - defend the body against the bone
shape easily/ ease marrow.
movement in small infection and diseases
blood capillary  monocytes and neutrophils are phagocytes which Function
 Important in
Function: engulf and digest bacteria
 Transport of carbon  lymphocytes become specialized as B cells and T blood clotting.

dioxide and oxygen in cells which produce the immune response against
the blood
foreign substances

 Divide into 2 group: 2) Granulocytes
1) Agranulocytes

ii. Plant cells and tissues
MERISTEMATIC TISSUE

MERISTEMATIC TISSUE
 Tissue that retain the ability to divide by mitosis to produce new cells. Thus, it is responsible for

plant growth.
 Features/Characteristics of meristematic tissue:

(a) Cell that undergo high mitotic rate/ actively divide by mitosis.
(b) Consist of undifferentiated/ unspecialized cell. Found in zones of the plant where growth can

take place.
(c) The cells have thin primary cell wall, small vacuoles, large nucleus and dense cytoplasm

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Types of meristems Distribution/ location Function
A. Apical meristem At root tips and shoot apex Give rise to primary tissues in the plant, for
growth/ elongation of plant either shoots or
(primary roots
meristem)

Shoot meristem Root meristem

GROUND TISSUE Parenchyma Collenchyma Sclerenchyma
Characteristics
Structure

Dead or live Living cell/ has nucleus Living cell/ has Dead cell at maturity/ no nucleus
Shape of cell nucleus
The cells are The cells are The cells are polygonal in shape,
Cell rounded/isodiametric in polygonal in shape, elongated with tapering ends.
arrangement shape with large central elongated cell The cells are irregular in shape-
vacuole sclereids.
Cells are loosely arranged Cells are closely Cells are closely/ tightly
with many intercellular air packed cells, with arranged with no intercellular
spaces. little or few space.
intercellular air
spaces.

Characteristics Parenchyma Collenchyma Sclerenchyma

Cell wall Thin primary cell walls Thicker primary Cell walls consist of primary cell
without secondary cell walls. cell walls, with walls and secondary cell walls
unevenly that thickened uniformly and
thickened at the lignified. Simple pits present in
corner of the cell secondary cell walls
(thickened by
cellulose and
pectin). No
secondary cell
walls.

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Types Only one type Only one type Two types of sclerenchyma:
fibers and sclereids (stone cells )
Location/
distribution In cortex, pith, packing Below epidermis in Fibers - vessel elements and
tissues in phloem and xylem stems, midrib of tracheid of xylem. (Hemp and
leaves jute in plant).
and petioles of
leaves. This allows Sclereids - Give hard structure
them to bend in the (testa of seed, shell of walnut,
wind. coconut) and gritty structure in
pears and guava.

Function - Packing tissues in stems Give mechanical Give mechanical strength,
and roots for support and strength and structural support and rigidity
turgidity flexibility/ elastic to the plant result of lignin
support. (allow cell deposition in secondary walls
- Potentially meristematic to expand as it Give protection from
(root and shoot tip) grows- stretchable) mechanical damage.
As supporting
- Allow gaseous exchange tissue in
- Storage organ for food herbaceous plant/
young parts of
storage (potato) plant/ soft and non-
- Site of photosynthesis woody plant organ.
- Secretion (eg: resin)

**Modified parenchyma:
epidermis, mesophyll,
endodermis, pericycle

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GROUND TISSUE

FIGURE 12: Parenchyma cells

FIGURE 13: Collenchyma cells

FIGURE 14: Sclerenchyma cells

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(c) VASCULAR TISSUE PHLOEM
Function: Transport organic substances from
XYLEM
Function: Transport water and mineral from leaves to all part of plant.

root to shoot

Tracheid Vessel element

Similarities of tracheid and vessel element: Similarities of sieve tube and companion cell:
 Both non-living/ dead cells  Unlignified cell walls
 Both have thick, lignified secondary cell walls  Both do not have pits
 Both have pits to allow lateral movement of water  Both are living cells
 Both function in transporting water and mineral
Differences of sieve tube and companion cell:
ions and act as supporting tissues.

Differences of tracheid and vessel element:

Tracheid Vessel element Sieve tube Companion cells
Has longer and Has shorter and wider Function in Function to assist sieve
narrower/smaller lumen transporting sugar tube.
lumen (sucrose) and organic Contain nucleus and
Cylindrical shape with Cylindrical shape with substances from lot of mitochondria to
tapering ends which less tapering ends leaves throughout provide energy for
is overlaps and (end wall forming plant loading sugar into
interlocked with one partially or completely sieve tube
another (no end plate perforated end wall) Large in diameter, Connected by
perforation) long tube with no numerous
More efficient in nucleus. Assist by plasmodesmata with
Less efficient in transporting water companion cells for sieve tube
transporting water functioning because Shorter and smaller
at maturity, most of with dense cytoplasm
the organelles are
degenerate. No perforated ends
Have perforated
ends forming sieve
plate

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2.4 CELL TRANSPORT

(a) Overview of various transport mechanisms across the membrane

TRANSPORT ACROSS MEMBRANE

PASSIVE TRANSPORT ACTIVE TRANSPORT
Follow concentration gradient Against concentration gradient

Not require energy/ ATP Require energy/ ATP

Simple diffusion Sodium-Potassium pump Bulk transport

Facilitated diffusion Endocytosis Exocytosis
Osmosis
Secretion of
Phagocytosis Pinocytosis enzymes and

hormones

Differences of passive and active transport

Passive transport Active transport
Movement of molecules follow/down Movement of molecules against concentration
concentration gradient (from higher gradient(from low concentration to high
concentration to low concentration of substances) concentration of substances)
Do not use energy in the form of ATP Use energy in the form of ATP
Do not used carrier protein except facilitated Need carrier protein
diffusion
Occur in both living and non-living cell Occur only in living cell

FIGURE 15: Various transport mechanisms across the membrane
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(i) PASSIVE TRANSPORT FIGURE 18: Simple Diffusion

PASSIVE TRANSPORT
i. Simple Diffusion

 Net movement of molecules down a concentration gradient
(from a region of higher concentration to lower concentration)
across a semi permeable membrane without energy/ ATP.

 Electrochemical gradient causes the molecules to move. It is
always occur until equilibrium is reached.

 Substances that can be transported:
 Lipid-soluble/ hydrophobic molecules such as steroids
 Small/ non-polar/ uncharged molecules, such as H2O, O2 and
CO2.

ii. Facilitated diffusion
 The transport of molecules across a semi permeable membrane

through channel or carrier protein down a concentration
gradient without energy requirement.

Channel protein Carrier protein FIGURE 19: Channel protein
Has fix shape with hydrophobic Have a specific binding
pore. site.
Allows selected charged Undergo rapid changes in
substances (usually ions or polar shape to transfer the
molecules) to pass through. molecule.
e.g. Na+ and K+ channel e.g. glucose

 Substances that can be transported:
 small/ large polar molecule like glucose, amino acid, sodium

ions, chloride ions FIGURE 20: Carrier protein

iii. Osmosis
 Osmosis is the net movement of water molecules from a region of high water potential to a region of

low water potential across selectively permeable membrane without using energy (ATP)

 Concept of water potential, ψ:
 Water potential (ψ) is the net tendency of water molecules to move freely across a membrane by

osmosis due the kinetic energy.
 Pure water at standard temperature (00C) and pressure (100 kPa) has water potential of 0 kPa.
 The presence of solutes will lower the water potential of solution, thus the ψ become –ve.
 It is because polar/ ionic solutes in the solution surrounded by polar water molecules. Therefore,

less free moving water molecules, less tendency water molecules to move and low ψ.
 As the conclusion, present of solute lowers water potential of a solution.

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FIGURE 16: Osmosis, movement of water molecules from a region of high water potential to a
region of low water potential

The effects of different solutions on animal and plant cell:

Types of cell Hypertonic solution Isotonic solution Hypotonic solution
and solution (concentrated solution) (equivalent (dilute solution)

Animal cell Shrivel/ crenated / concentration) Haemolysed (Erythrocytes)/
Normal Lysed /Swell and burst

ψcell = ψs shrink

Plant cell Plasmolysed Flaccid Turgid
ψcell = ψs +

ψp

Plasmolysis: shrinking of protoplasm from the cell wall of a plant due to excessive water loss from cell.
Hemolysis: bursting/ lysis of a red blood cell as the cell swell excessively.

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(ii) ACTIVE TRANSPORT

ACTIVE TRANSPORT
 Active transport is the movement of ions/ molecules/ substances across a semi-permeable

membrane against a concentration gradient (from lower concentration to higher concentration) by
using energy in the form of ATP.
 It also uses a specific carrier protein for movement of small and / or large polar molecule/ ion.

FIGURE 17: Active transport

 Example:

1. Uptake of mineral salt by root hairs

2. Uptake of glucose by the cells in intestine

3. Sodium-potassium pump
 Maintains the gradient of sodium (Na+) and potassium ions (K+) across the membrane

 Na+ and K+ need to be transported by active transport because both are lipid

insoluble/charges/hydrophilic substance/ion//the phospholipid layer/membrane is impermeable

to Na+ and K+
 The hydrophobic tails/region in the phospholipid bilayer repel the ions

Mechanism of sodium potassium
pump:

i. Three sodium ions in cytosol bind

to the carrier protein.

ii. Phosphate group is transferred

from ATP to carrier protein.

iii. Phosphorylation causes the

carrier protein to change its
conformation. It causes the 3 Na+

to be released out of the cell.

iv. Two K+ ions bind to the carrier

protein.
v. K+ binding triggers the release of

FIGURE 18: Na+ - K+ pump a phosphate group

(dephosphorylation of protein).

vi. The loss of a phosphate group

restores the protein to return to its
original conformation. 2K+ is

released into the cell and the

cycle repeats. 38 | P a g e

BASIC UNDERSTANDING OF BIOLOGY FOUNDATION SEM 1: DB014

Bulk transport
 Bulk transport is the transport of large particles into and out of the cell.

i. Bulk transport :Endocytosis
 Endocytosis is the uptake of particles by the cell via invagination of plasma membrane.

i. Pinocytosis ii. Phagocytosis

 Process whereby a cell takes up dissolved  Process whereby a cell takes up solid particles

particles and macromolecules. and large molecules.

 The cell ingests extracellular fluid or  Cell engulfs large solid particles by wrapping

dissolved materials. pseudopodium around the particle and forming a

 Tiny pinocytic vesicles are formed as the food vacuole (phagosome).

plasma membrane invaginates inward and  Lysosome will fuse with the food vacuole

pinches off. (phagosome) and release its hydrolytic enzyme to

 Liquid contents of the vesicle are then slowly digest the content/ particle.

transferred to the cytoplasm and the process  The nutrients then absorbed into cytoplasm

does not involve lysosome.  Examples:
 Phagocytes (leucocytes) engulf foreign
 Example:
 Reabsorption of amino acids by the substances like bacteria.
 Amoeba engulf food particles.
proximal tubule in nephron (kidney

tubule).

ii. Bulk transport :Exocytosis
 The transport of material out of the cell within

membrane-bound vesicles.
 The membrane-bound vesicles fuse with the

plasma membrane, releasing their contents to
the exterior.
 Example:

 Removal of waste material from the cell
 Secretion of mucus by goblet cells
 Hormones and digestive enzymes are

secreted by exocytosis from the secretory
cells of the intestine and endocrine
glands.

END OF TOPIC

39 | P a g e