Chapter 6 : Nutrition In Plants

Question 1

What are autotrophs

Answer 1

Living things that are able to Synthesise their food by the process of photosynthesis

Question 2

What is photosynthesis ?

Answer 2

It is the process where light energy absorbed by the chlorophyll is converted into chemical energy

Question 3

Chemical equation for photosynthesis, what are the conditions needed for photosynthesis

Answer 3

6CO2 + 6H20 —> C6H12O6 +6O2. Presence of light and chlorophyll

Question 4

What happens during the light dependent stage (3)

Answer 4

1. Absorption of light energy by chlorophyll
2. Conversion of light energy to chemical energy
3. Photolysis of water

Question 5

What happens in the light independent stage

Answer 5

Hydrogen atoms produced from the photolysis of water are used to reduce CO2 to form glucose by a series of enzymatic reactions

Question 6

Name the 3 factors affecting rate of photosynthesis

Answer 6

1. Light intensity
2. CO2 Conc
3. Temperature

Question 7

Why is there an optimum temperature for photosynthesis

Answer 7

Light independent and, to a certain extent, light dependent reactions involve enzymes which are temperature sensitive. If the temperature increases above the optimum temperature, the enzymes would rapidly denature

Question 8

What is glucose used for in the plant ? (4)

Answer 8

1. Cellular respiration and formation of cellulose cell walls
2. Used to form fats (for storage, cellular respiration, synthesis of new protoplasm)
3. Used to form amino acids and proteins (reacts with nitrates and mineral salts to form proteins, essential for synthesis of new protoplasm )
4. Converted into sucrose (stored in storage organs) or starch in leaves

Question 9

State the function of the
a) lamina (leaf blade)
b) Petiole

Answer 9

A) lamina or the leaf blade as a large surface area which maximise absorption of sunlight. It also allows for rapid diffusion of carbon dioxide into the inner cells of the leaf.
B) Petiole positions the lamina for maximum absorption of sunlight and gaseous exchange

Question 10

State the parts of the leaf from top to bottom (7)

Answer 10

Cuticle
Upper epidermis
Palisade mesophyll
Spongy mesophyll
Vascular bundle (containing xylem and phloem)
Lower epidermis
Guard cells / stoma

Question 11

Function of the cuticle ?

Answer 11

It is a waxy layer above the epidermis which prevents excessive water loss.
Transparent to allow sunlight to penetrate into the mesophyll layer

Question 12

Why are there air spaces in the spongy mesophyll layer ? How does CO2 diffuse into the cell ?

Answer 12

To allow for rapid diffusion of gases into the leaf which increases.
There is a thin film of water surrounding the mesophyll cells which the CO2 dissolves in and diffuses into the cells

Question 13

How do guard cells control the opening and closing of the stoma

Answer 13

When opening
1. Guard cells take up potassium ions by active transport. This decreases water potential in the guard cell and causes water to enter the guard cell through osmosis which causes the cell to curve as they become turgid.

When closing
1. K+ ions are pumped out of the cell and the water flows out of the guard cell through osmosis. The stoma the closes as the guard cells become flaccid