Biology pt.2

Question 1

What is Photosynthesis?

Answer 1

Photosynthesis is a series of chemical reactions that we can summarise using a word equation. Energy and chlorophyll are needed for it to happen. The energy is transferred by
light (usually from the Sun) and becomes stored in glucose.

Question 2

Photosynthesis equation:

Answer 2

carbon dioxide + water  glucose + oxygen

Question 3

Getting carbon dioxide

Answer 3

Air, containing carbon dioxide, diffuses into leaves through small holes called stomata. Leaves are thin so that the carbon dioxide does not need to go very far before reaching the cells that need it.

Question 4

Increasing what would speed up photosynthesis?

Answer 4

Increasing the amount of carbon dioxide around a plant can often speed up photosynthesis.

Question 5

How do leaves get light?

Answer 5

Many leaves are wide so that they have a large surface area to trap as much light as possible.
They are also arranged so that they do not shade one another.

Question 6

Where does most photosynthesis happen?

Answer 6

in the palisade cells, which are found near the upper surface of leaves. Palisade cells are packed with chloroplasts. Chloroplasts contain chlorophyll, a green
chemical that absorbs energy transferred by light and uses it to power photosynthesis. Increasing the amount of light can often speed up photosynthesis.

Question 7

Aerobic respiration

Answer 7

Plant cells release the energy stored in glucose using aerobic respiration (another series of chemical reactions):
glucose + oxygen  carbon dioxide + water

Question 8

What are the 3 things glucose is used for?

Answer 8

● respiration to release energy
● making other substances that act as stores of energy (e.g. starch), which can be turned back
into glucose for respiration when needed
● making new materials for growth, e.g. cellulose (for cell walls), lipids (e.g. for cell membranes)
and proteins (e.g. for enzymes). To make proteins, mineral salts called nitrates are needed.

Question 9

Breeding variety:

Answer 9

Farmers and plant breeders may choose or ‘select’ a plant with certain characteristics.
This organism is then used to breed from. The offspring that have the best of these characteristics
are then bred from again. This is called selective breeding and is how many varieties are created.

Question 10

What is cross-breeding?

Answer 10

Sometimes two different varieties are bred together to try to produce offspring with characteristics
from both varieties.