Respiration In

Plants

Energy requirement in plants

• The energy requirement for living processes of plants is lower compared to animals. Why?

Because plants are less active than animals. Plants do not move about like animal do.

The Intake Of Oxygen By Plants For Respiration

• Plants do not have specialised breathing mechanisms for gaseous exchange.

• Gaseous exchange between plants cells and the environment occurs by diffusion through stomata and lenticels.

stomatastomata

lenticelslenticels

Gaseous exchange in the light

• When the leaf is photosynthesising,

CO2 concentration ↑ in the air spaces of the spongy layer. (what will happen?)

O2 diffuses from the atmosphere through stomata into the leaf for cell respiration.

Gaseous exchange in the dark

• Respiration alone is taking place.

< O2 in the air spaces than atm. O2 diffuses inward though lenticels. Stomata are normally closed at night.

CO2 will diffuse outwards.

Aerobic & Anaerobic Respiration

in Plants.

C6H12O6 + 6O2 6CO2 + 6H2O + Energy

2880 kJ / m

C6H12O6 2C2H5OH + 2CO2 + Energy

210 kJ / m

Aerobic @ Anaerobic ?

Aerobic respiration in plants

• Need O2, waste products are CO2 and water.

• In the light, photosynthesis is faster than

respiration. The CO2 produced is quickly used

up by photosynthesis.

• In the dark, respiration continues.

Anaerobic respiration in plants

• Yeast respires anaerobically to produce alcohol (alcoholic fermentation).

• During flooding, plants can survive for several days completely submerged in water.

• Young rice plants are planted in fields that are muddy and flooded.

• During initial stages of germination, embryo is completely enclosed within an airtight seed coat.

Respiration & Photosynthesis

• Respiration is the reverse of photosynthesis.

Compare & Contrast Respiration & Photosynthesis

Respiration Photosynthesis

Similarities

• Both take place in living cells. • Both are metabolic process.

Respiration PhotosynthesisA process of

catabolism (breaking down of organic

materials)

A process of anabolism

(synthesis of organic materials)

Occurs in all living cells

Occurs in cells containing chlorophyll.

Take place in the presence / absence

of light

Takes place only in the presence of light

Differences

Respiration Photosynthesis

Uses glucose and oxygen

Uses carbon dioxide and water

Produces carbon dioxide and water

Produces glucose and oxygen

Respiration Photosynthesis

Chemical energy is converted into heat and energy ATP.

Solar energy is converted into

chemical energy

Cell loses weight Cell gains weight

Light Intensity

& The

Compensation

Point

CO2 concentrations in air around plants throughout the day

CO2 O2

Day

O2 CO2

night

O2 CO2

All the CO2 produced during respiration is reused during photosynthesis

Compensation point

Light intensity

The Compensation Point

The light intensity at which the rate of carbon

dioxide production during respiration is equal to that of carbon dioxide consumption during

photosynthesis.

If the rate of photosynthesis and the rate of respiration remained at compensation point:

• The plant would not be able to store food.

• There would be no growth and development in green plants.

• No oxygen released into the atmosphere to sustain living things.