Topic 7 - Photosynthesis and Food Production

Question 1

Photosynthesis

Answer 1

the process by which plants make their own food by converting light energy from the sun into chemical energy, which is stored in the glucose

Question 2

Adaptations of leaves for photosynthesis

Answer 2

• broad and flat to increase surface area for sunlight absorption
• chloroplasts are found in the palisade layer, so they’re near the top where they can get the most light
• upper epidermis is transparent so light can pass through to the palisade layer
• vascular bundles transport water and nutrients to every part of the leaf
• waxy cuticle helps reduce water loss by evaporation

Question 3

Light limiting factor

Answer 3

as light intensity increases, the rate of photosynthesis increases up to a certain point where temperature or CO2 becomes the limiting factor

Question 4

Carbon dioxide limiting factor

Answer 4

as carbon dioxide concentration increases, the rate of photosynthesis increases up to a certain point where temperature or light becomes the limiting factor

Question 5

Temperature limiting factor

Answer 5

as temperature increases, the rate of photosynthesis increases up to a point. If the temperature is over 45˚C, enzymes denature and rate of photosynthesis decreases

Question 6

Testing a leaf for starch

Answer 6

1. Heat leaf in boiling water for 10 seconds to denature the enzymes and stop chemical reactions
2. Put the lear into a test tube of alcohol. Stand test tube in the beaker of hot water for 10 mins. This will decolourise the leaf
3. Rinse leaf in water to remove alcohol and rehydrate it
4. Put leaf in white tile cover with iodine solution
5. A blue/black colour shows that starch is present

Question 7

Nitrates

Answer 7

Contain nitrogen for making amino acids and proteins, which are needed for cell growth. If a plant can’t get enough nitrates, leaves will turn yellow

Question 8

Phosphates

Answer 8

Contain phosphorus for making DNA and cell membranes. They’re needed for respiration and growth. Deficiency causes poor root growth and their older leaves are purple

Question 9

Potassium

Answer 9

Help enzymes needed for photosynthesis and respiration. Deficiency leads to poor flower/fruit growth and discoloured leaves

Question 10

Magnesium

Answer 10

Needed to make chlorophyll. Deficiency leads to yellow leaves

Question 11

Xylem

Answer 11

Carry water and mineral salts from the roots to the leaves

Question 12

Phloem

Answer 12

Transports sugar and amino acids to different parts of the plant

Question 13

Adaptations of leaves for gas exchange

Answer 13

• Thin (short diffusion distance for gases)
• Broad (large surface area for diffusion)
• Air spaces allow gases to move easily between cells
• Stomata control diffusion of CO2 and oxygen
• Guard cells control the opening and close of stomata

Question 14

Fertilisers

Answer 14

substances that provide essential minerals for plant growth to increase crop yield

Question 15

How to create ideal conditions for photosynthesis

Answer 15

• enclosing plants in glasshouses or polythene tunnels keep them free from pests and disease
• artificial light is supplied after dark to give plants more time to photosynthesise
• increasing the level of carbon dioxide (e.g. by using a paraffin heater)
• increasing temperature by using thermostat heaters and fans
• increasing level of water by using a sprinkler system
• soil pH control - add limestone to increase pH and peat to decrease pH

Question 16

Pesticide

Answer 16

Chemicals sprayed on crops to kill pests that can also accidentally kill other wildlife (e.g. bees)

Question 17

Advantages of chemical pesticides

Answer 17

• quick + easy
• increases crop yield
• avoid problems associated with introducing a new predator (e.g. cane toad)

Question 18

Disadvantages of chemical pesticides

Answer 18

• pollutes water and soil
• kills other harmless organisms (reduction of biodiversity)
• affects the health of humans
• bioaccumulation of toxins as you go up the food chain
• pesticide resistance to create super pests

Question 19

Advantages of biological control

Answer 19

• Long lasting (don’t need to reapply)
• No bioaccumulation
• Specific to the pest you want to kill

Question 20

Disadvantages of biological control

Answer 20

• Can’t control where they go
• Not localised
• Can outcompete native species (e.g. for food)

Question 21

Hydrogen carbonate indicator

Answer 21

Used to show carbon dioxide concentration in a solution
- Purple = low CO2 level = photosynthesis > respiration
- Red = atmospheric level = photosynthesis = respiration
- Yellow = high CO2 level = photosynthesis < respiration

Question 22

Chlorophyll

Answer 22

A photosynthetic pigment in chloroplasts that absorbs light energy for photosynthesis

Question 23

Waxy cuticle

Answer 23

The top layer of a leaf that prevents evaporation of water from the surface of the leaf

Question 24

Limiting factor

Answer 24

a variable that, when in short supply, reduces the maximum rate of photosynthesis

Question 25

Stoma

Answer 25

a part of the leaf that controls gas exchange

Question 26

Leaf

Answer 26

an organ of the plant that produces food for the plant through photosynthesis

Question 27

Biological controls

Answer 27

The introduction of an animal to a crop field to kill pests by predating them

Question 28

Bioaccumulation

Answer 28

when toxins build up (accumulate) in a food chain

Question 29

epidermis

Answer 29

A single layer of cells that covers the leaf. It provides a protective barrier against mechanical injury and infection

Question 30

Iodine

Answer 30

an indicator that turns from orange-brown to blue-black in the presence for starch

Question 31

chloroplast

Answer 31

the site of photosynthesis in a palisade cell

Question 32

plant pest

Answer 32

something that can directly or indirectly injure, cause damage to, or cause disease in a plant