Review Question

• Which mode of nutrition do the green plants

carry out?

A. Autotrophic nutrition

B. Heterotrophic nutrition

Overview of nutrition in green plants

carbon dioxide and water

photosynthesis

carbohydrates (e.g. glucose) mineral salts

(e.g. NO3-, SO4

2-)

water fatty acids glycerol amino acids

nutrients for plants can be used to produce all

plant materials (e.g. enzymes, cell wall,

cytoplasm, cell membrane, chlorophyll)

Nature of photosynthesis

• Anabolic process

• Takes place in chloroplast

• Necessary factors :

•Carbon dioxide

•Water

•Sunlight

•Chlorophyll

Light

Light Absorption Spectrum

Why leave looked green?

Different pigments in absorption

spectrum

How light energy used?

Light reaction • Light energy is trapped by chlorophyll in

chloroplast

Light reaction Light energy absorbed by chlorophyll splits water molecules into

hydrogen and oxygen

Light reaction Oxygen is released as a gas through stoma to outside

Light reaction Hydrogen is fed into dark reaction

Dark reaction

• No light is required; can take place either in

light or darkness

Hydrogen produced in light reaction combines with CO2 to form

carbohydrates

Water is formed as a by-product

Chlorophyll Structure

Light Reaction

Photophosphorylation

Cyclic photophosphorylation

Dark Reaction

M. Calvin

Calvin Cycle

CHLOROPLAST

Predicted folding pattern of the D1 protein of the PSII reaction center.

Fate of product of photosynthesis

Kreb cycle

Factors affect rate of

photosynthesis

Expt. Show effect of factors

Distance

Heat

Conc. Of

NaHCO3

Fate of carbohydrate products in

the plant carbon dioxide and water

photosynthesis

carbohydrates (e.g. glucose) mineral salts

(e.g. NO3-, SO4

2-)

water fatty acids glycerol amino acids

carbohydrates (e.g. glucose)

Fate of carbohydrate products in

the plant carbon dioxide and water

photosynthesis

mineral salts

(e.g. NO3-, SO4

2-)

water fatty acids glycerol amino acids

release energy by respiration

carbohydrates (e.g. glucose)

Fate of carbohydrate products in

the plant carbon dioxide and water

photosynthesis

mineral salts

(e.g. NO3-, SO4

2-)

water fatty acids glycerol amino acids

convert into starch for storage

Fate of carbohydrate products in

the plant carbon dioxide and water

photosynthesis

carbohydrates (e.g. glucose) mineral salts

(e.g. NO3-, SO4

2-)

water fatty acids glycerol amino acids

change into sucrose and is transported

to other parts through phloem

Fate of carbohydrate products in

the plant carbon dioxide and water

photosynthesis

carbohydrates (e.g. glucose) mineral salts

(e.g. NO3-, SO4

2-)

water fatty acids glycerol amino acids

combine to form fats and oils to form

cell membranes and as a food store

Fate of carbohydrate products in

the plant carbon dioxide and water

photosynthesis

carbohydrates (e.g. glucose) mineral salts

(e.g. NO3-, SO4

2-)

water fatty acids glycerol amino acids

join together to become

protein molecules

Importance of photosynthesis

• It is the only method to convert energy in

sunlight into chemical energy

– Animals have to depend on plants for food

supply

– Plants: producers; animals : consumers

• To maintain a constant oxygen level in the

atmosphere

Experiments to test for necessary factors

of photosynthesis

• Experimental set-up: To remove the factor

under study and to see if photosynthesis still

takes place

• Control set-up: Identical to experimental

set-up except that the missing factor is

present

A set-up to study whether light is

necessary for photosynthesis

water

leafy shootRegion A

Region B

Which is the control, the exposed region

A or the shaded region B?

To show that photosynthesis cannot take place in the absence of

light

What is the purpose of setting up

region A?

• As a control

Too simple and not explicit!

Destarching

• Reason:

– To avoid any existing starch in the leaves

interfering with the result, and to show that any

starch found after the experiment was produced

during the period of investigation

• Method:

– By placing the plant in dark for at least 24

hours

Parts of plant where

photosynthesis takes place

• Places where chloroplasts are found

• Mainly in the leaf because

– it contains a lot of chloroplasts

– it is well adapted for performing photosynthesis

Cross-section of a dicot leaf upper

epidermis

protect internal tissues from mechanical damage and bacterial and fungal invasion

Cross-section of a dicot leaf Cuticle • a waxy

layer • prevent

water loss from the leaf surface

Cross-section of a dicot leaf

mesophyll

Cross-section of a dicot leaf

palisade

mesophyll

columnar cells closely packed together

absorb light more efficiently

contains many chloroplasts

Cross-section of a dicot leaf

spongy

mesophyll

irregular cells loosely packed together to leave numerous large air spaces allow rapid diffusion of gases throughout the leaf

less chloroplasts for photosynthesis

Cross-section of a dicot leaf

lower

epidermis

same as upper epidermis except the cuticle is thinner

Cross-section of a dicot leaf

stoma opening which allows gases to pass through it to go into or out of the leaf

Cross-section of a dicot leaf

guard cells control the size of stoma

Cross-section of a dicot leaf

vascular bundle (vein)

Cross-section of a dicot leaf

xylem •to transport water and mineral salts

towards the leaf

Cross-section of a dicot leaf

phloem •to transport organic substances

away from

the leaf

Adaptation of leaf to

photosynthesis Upper epidermis and cuticle is transparent Allows most light to pass to photosynthetic mesophyll tissues

Adaptation of leaf to

photosynthesis

Palisade mesophyll cells are closely packed and contain many chloroplasts To carry out photosynthesis more efficiently

Adaptation of leaf to

photosynthesis

Spongy mesophyll cells are loosely packed with numerous large air spaces To allow rapid diffusion of gases throughout the leaf

Adaptation of leaf to

photosynthesis

Numerous stomata on lower epidermis To allow rapid gaseous exchange with the atmosphere

Adaptation of leaf to

photosynthesis Extensive vein system

•Allow sufficient water to reach the cells in the leaf

•To carry food away from them to other parts of the plant

The end