Chapter 4 - Nutrition in Plants

Question 1

What is photosynthesis?

Answer 1

The process in which light energy is absorbed by chlorophyll and converted into chemical energy
(requires inorganic molecules such as carbon dioxide and water for the synthesis of organic molecules such as glucose)

Question 2

What is the chemical energy produced in photosynthesis used for?

Answer 2

The chemical energy is used to synthesise carbohydrates from water and carbon dioxide.

Question 3

What occurs in the light-dependent stage (light stage)?

Answer 3

• Light energy is absorbed by chlorophyll and converted to chemical energy
• Photolysis of water: light energy is used to split water to form H+ ions and oxygen gas

Question 4

Equation for photolysis of water

Answer 4

12H2O → 6O2 + 24H+

Question 5

What occurs in the light-independent stage (dark stage)?

Answer 5

• H+ ions produced from the photolysis of water are used to reduce carbon dioxide to form glucose by a series of enzyme reactions

Question 6

Equation for Calvin cycle

Answer 6

6CO2 + 24H+ → C6H12O6 + 6H2O

enzyme-controlled reactions

Question 7

Overall chemical equation of photosynthesis

Answer 7

6CO2 + 12H2O –light energy, chlorophyll–> C6H12O6 + 6O2 + 6H2

Question 8

Overall word equation of photosynthesis

Answer 8

carbon dioxide + water –light energy, chlorophyll–> glucose + oxygen + water

Question 9

Conditions essential for photosynthesis

Answer 9

sunlight, chlorophyll, carbon dioxide, suitable temperature (for enzyme activity), water

Question 10

What is a limiting factor?

Answer 10

A factor that directly affects or limits a process if its quantity or concentration is altered

Question 11

Factors affecting rate of photosynthesis

Answer 11

light intensity
temperature
carbon dioxide concentration

Question 12

Effect of light intensity on the rate of photosynthesis

Answer 12

Rate of photosynthesis increases as light intensity increases (until light intensity is no longer a limiting factor)

Question 13

Effect of temperature on the rate of photosynthesis

Answer 13

• At low temperatures, rate of photosynthesis is slow as enzymes are less active
• At higher temperature, rate of photosynthesis increases as enzymes become more active
• At optimum temperature, rate of photosynthesis is maximum as enzymes are most active
• At extreme temperatures higher than optimum temperature, rate of photosynthesis slows down as enzymes are denatured

Question 14

Effect of carbon dioxide concentration on the rate of photosynthesis

Answer 14

Rate of photosynthesis increases as carbon dioxide concentration increases (until carbon dioxide concentration is no longer a limiting factor)

Question 15

Fate of glucose in leaves (1): immediate uses

Answer 15

Used immediately by plant cells for cellular respiration or to form cellulose cell walls (made up of glucose)

Question 16

Fate of glucose in leaves (2): storage

Answer 16

Excess glucose is temporarily stored as starch in leaves

Question 17

Fate of glucose in leaves (3): transport

Answer 17

Converted into sucrose which is transported to storage organs

Question 18

Why is sucrose used as a form of transport?

Answer 18

Sucrose is a non-reducing sugar: will not reduce (take away O2 from) other molecules as it is transported

monosaccharide (glucose) → disaccharide (sucrose)

Question 19

Fate of glucose in leaves (4): amino acids

Answer 19

Reacts with nitrates and mineral salts to form amino acids → form proteins for synthesis of new protoplasm in the leaf
Excess amino acids are transported away for synthesis of new protoplasm or for storage as proteins

Question 20

Fate of glucose in leaves (5): fats

Answer 20

Used to form fats for storage, cellular respiration or synthesis of new protoplasm

Question 21

Importance of photosynthesis: food and energy

Answer 21

Plants are producers in the food chain. Chemical energy stored in plants is transferred to other organisms through feeding.
*can convert light energy to chemical energy

Question 22

Importance of photosynthesis: oxygen and carbon dioxide

Answer 22

Helps to purify air by removing carbon dioxide from the atmosphere and releasing oxygen as a by-product
*maintains a constant level of oxygen and carbon dioxide in the atmosphere

Question 23

Importance of photosynthesis: fossil fuels

Answer 23

Energy stored in fossil fuels (coal, oil, gas etc) is captured through photosynthesis
(this energy can be released and used through burning fossil fuels)

Question 24

Lamina (leaf blade)

Answer 24

large surface area to maximise absorption of sunlight

allows rapid diffusion of carbon dioxide to reach inner cells

Question 25

Petiole

Answer 25

positions lamina for maximum absorption of sunlight and gaseous exchange

Question 26

Veins

Answer 26

allow transport of water and mineral salts to the cells in the lamina transport manufactured food from the leaves to other parts of the plant - branch vein - branch of mid-rib - mid-rib

Question 27

Leaves

Answer 27

usually arranged in a regular pattern around the stem paired arrangement / alternate arrangement: ensures that leaves are not blocking one another and each leaf receives optimum amount of light

Question 28

Cuticle

Answer 28

waxy layer above the epidermis (wax: fats formed from glucose) prevents excessive water loss through evaporation transparent to allow sunlight to penetrate to the mesophyll

Question 29

Upper epidermis

Answer 29

single layer of closely packed cells | not really used for photosynthesis, more for structural purposes

Question 30

Palisade mesophyll

Answer 30

a few layers of closely packed cells | cells are long, cylindrical and contain numerous chloroplasts for maximum absorption of light

Question 31

Spongy mesophyll

Answer 31

irregularly shaped cells | numerous intercellular air spaces for rapid diffusion of gases inside the leaf

Question 32

Vascular bundle

Answer 32

xylem and phloem | transport of water and food materials within the plant

Question 33

Lower epidermis

Answer 33

single layer of closely packed cells | stomata are found here

Question 34

Stomata and guard cells: during the day

Answer 34

1. Water from adjacent epidermal cells enters guard cells (via osmosis) 2. Guard cells swell and become turgid → becomes curved and pulls stoma open

Question 35

During the day, cell sap of guard cells has more negative water potential than surroundings because...

Answer 35

- contains more glucose from photosynthesis - triggers even more photosynthesis as stomata open and more CO2 enters - other ions (e.g. K+) are pumped in to increase negativity of WP of cell sap

Question 36

Stomata and guard cells: at night

Answer 36

1. K+ (and other) ions diffuse out of guard cells 2. WP in guard cells increases → water exits by osmosis 3. Guard cells become flaccid → stoma closes

Question 37

Entry of water into leaf

Answer 37

1. Water is brought to the leaves via the xylem vessels in the veins 2. Water leaves the veins and moves from cell to cell in the mesophyll by osmosis

Question 38

Entry of CO2 into leaf: during the day

Answer 38

1. CO2 is rapidly used up during photosynthesis 2. CO2 concentration inside the leaf is lower than atmospheric air 3. CO2 DIFFUSES into leaf via stomata 4. CO2 dissolves into the film of water surrounding the mesophyll cells and diffuses into the cells

Question 39

What is the absorption spectrum?

Answer 39

A graph of relative absorbance of different wavelengths of light by a photosynthetic pigment

Question 40

What is the action spectrum?

Answer 40

A graph of relative photosynthetic rates at different wavelengths of light