TOPIC 6 PLANT PHYSIOLOGY_JACQUELINE JOSEPH

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chapter

AGR022
Basic Plant Science

Chapter 6: PHYSIOLOGY OF PLANT

1 Chapter 6: PHYSIOLOGY OF PLANT 13-Dec-2021

CHAPTER OUTLINE BASIC PLANT
SCIENCE

AGR

6.1 Chemical processes of photosynthesis
6.2 Cellular respiration
6.3 Important of photosynthesis and cellular
respiration
6.4 Transpiration process

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CHAPTER LEARNING BASIC PLANT
OUTCOMES SCIENCE

At the end of this topic, the student should be able to: AGR

DEFINE the photosynthesis cellular respiration
and cellular respiration in plant

EXPLAIN the processes of photosynthesis, and
respiration

DEFINE and Explain transpiration process

DETERMINE the types of transpiration

3 25-Oct-21

1. PHOTOSYNTHESIS

 Photosynthesis is the process by which
autotrophic organisms use light energy to
make sugar and oxygen gas from carbon
dioxide and water

Question:

Where does
photosynthesis

take place?

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 Autotrophs – Plants

 produce their own food (glucose)
 Process called photosynthesis
 Mainly occurs in the leaves:

a. stoma - pores
b.mesophyll cells

Mesophyll Chloroplast
Cell
Stoma
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Internal Structure of a Leaf

• Stoma - (plural stomata)
a pore (or opening) in a
leaf where water vapor
and other gases leave
and enter the plant.

• Guard cell - one of a pair
of sausage-shaped cells
that surround a stoma
causing it to open and
close



E D
C
B
A

Actual image of chloroplasts

Chloroplast

Organelle where photosynthesis
takes place.

Stroma Thylakoid Granum
Outer Membrane
Inner Membrane

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Question:

Why are
plants
green?

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Chlorophyll Molecules

 Located in the thylakoid membranes
 Plants are green because the green

wavelength is reflected, not absorbed.

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 The pigments present in thylakoid
membranes consist largely of two kinds of
green chlorophylls, chlorophylls a and
chlorophylls b

 Pigments are molecules that absorb
certain wavelengths of light and transmit
others

 Chlorophyll a absorbed the red light and
the blue light and it is the most abundant
pigments in plants

 Chlorophyll b absorbed only blue light
and transmitted green light, thus the

leaves look green

Light Reflected
light

Chloroplast

Absorbed
light

Transmitted
light



Factor affecting rate of
photosynthesis

1. Light intensity

 Green plants require sunlight to carry out
photosynthesis

 The most effective light for photosynthesis is red
and blue light

 The light intensity influenced the light reaction in
photosynthesis

 If there is not limited factors, the rate of
photosynthesis is increase followed the light
intensity

Cont….

2. Temperature

 The rate of photosynthesis is maximum at the
room temperature or medium temperature of 20o
– 35oC

 If the temperature above of 40oC will
denaturalized the enzyme and the
photosynthesis slowly stopped

Cont…

3. CO2 concentration

 The rate of photosynthesis is directly proportional
to the carbon dioxide concentration

 The concentration of CO2 in the atmosphere is
only 0.035%. When value increase, the rate of
photosynthesis also increase until a maximum
level 1.0%. A concentration of CO2 that exceeds
1.0% will stimulate the closing of the stomata and
will reduce the rate of photosynthesis.

2. RESPIRATION

 Respiration - the process of releasing
or producing energy from the organic
molecule

 Living organism obtain their energy from
respiration to carry out life process

 Occur in mitochondria

Type of Cellular Respiration

1. Aerobic respiration

 Process of oxidation of organic compound that
require the oxygen

C6H12O6 + 6O2 6CO2 + 6H2O + 36 ATP

2. Anaerobic respiration

 Process of oxidation of organic compound without
the oxygen

 Fermentation process

C6H12O6 2C2H5OH + 2CO2 + 2ATP

Adenosine Triphosphate (ATP)

 ATP is a nucleotide molecule

 It was produce from the combination of
Adenine, Ribose and 3 molecule of
phosphate

 ATP acts as a temporary energy store.

 When ATP is hydrolysed, adenosine
diphosphate (ADP) and phosphate (Pi) are
produced and energy is released to carry out
cellular activities

Anaerobic Respiration

 Occur under anaerobic respiration, where no
molecule of oxygen

 Glucose is most completely break down to CO2 and
water because lack of oxygen

 But glucose was break down to ethanol (plant) and
CO2 or lactic acid (animal)

 Two type of anaerobic respiration (fermentation
process) : 1) Alcoholic fermentation
2) Lactic acid fermentation

Alcoholic fermentation

Glucose 2 ethanol + 2 CO2 + 2 ATP

Lactic acid fermentation

 Lactate accumulation in the muscles causes
cramping. The oxygen that is required to
break down the lactate.

Glucose 2 lactate + 2 ATP

3. TRANSPIRATION

GUTTATION : WATER EXPELLED IN FORM OF
DROPLETS FROM THE LEAVES

INTRODUCTION

• A PROCESS RELEASE OR LOSING LARGE AMOUNT OF WATER
THAT ABSORB BY THE ROOT IN THE FORM OF VAPOR

• OCCUR THROUGH;
(i) STOMATA OF LEAVES
(ii) CUTICULAR
(iii) LENTICEL-OPENING IN THE CORK
TISSUE SURFACE CALLED LENTICULAR
TRANSPIRATION

• TRANSPIRATION THAT OCCUR IN STOMATAL PORES MORE
IMPORTANT,COMPARE TO LENTICEL AND CUTICLE

Stomatal transpiration

Lenticel
Cuticle transpiration transpiration

THE FACTOR AFFECTING TRANSPIRATION
RATES

• AFFECTING BY 2 FACTOR;

(i) MORPHOLOGY FACTOR
(ii) ENVIRONMENTAL FACTOR

• THIS FACTORS AFFECTING TANSPIRATION
RATES BY STOMATAL



ENVIRONMENTAL FACTORS

• DURING TRANSPIRATION, DIFFISION OF WATER VAPOUR
OCCURS ALONG A WATER POTENTIAL GRADIENT

• FACTORS THAT INCLUDE;
(i) TEMPERATURE
(i) RELATIVE HUMIDITY
(iii) AIR MOVEMENT
(iv) LIGHT
(v) SOIL CONDITION

MORFOLOGY FACTORS

• THE MORFOLOGICAL FEATURES CAN AFFECTING THE RATES
OF TRANSPIRATION SUCH AS;

(i) CUTICLE

IF THE CUTICLE LAYER ARE THICK ,HENCE WATER OUT
TROUGH IT WILL DECREASE,SO IT AVOID LOSE WATER

(ii) DISSEMINATION STOMATES

THE POSITION OF STOMTES THAT ONLY HAVE BELOW THE
LEAVES SURFACE,AVOID FROM THE LIGHT

(iii) HABITUAL STOMATES

- OPENING AND CLOSING STOMATA ONLY
OCCUR,WHEN THERE ARE PRESSURE TUGOR
CHANGING INSIDE THE GUARD CELLS

(iv) STOMATA SUNK INTO LEAF

-IN CERTAIN PLANTS, STOMA EMBEDDED UNDER THE
SURFACE OR LOCATED IN THE HOLE,CONDITION IIN
THE HOLE IS MORE HUMID THAN ATMOSPHERE,
THIS DECREASE THE RATE OF TRANSPIRATION

(v) LEAF COVERED BY HAIR EPIDERMIS

-IN SOME SPECIES OF PLANT,THE LEAF HAVE HAIR

THAT CAUSE HUMID CONDITION AROUND THE
STOMA

-SO,THE RATE OF TRANSPIRATION IS DECREASE







IMPORTANT OF TRANSPIRATION

• TO HELP WATER AND MINERALS
TRANSPORTATION

• TO DECREASE LEAF TEMPERATURE
• NATURAL COOLING SYSTEM FOR PLANT