B8 Photosythesis

Question 1

Photosynthesis

Answer 1

The process by which plants make food using carbon dioxide, water, and light.

Question 2

Lipids

Answer 2

Plants and algae use some of the glucose from photosynthesis and energy transferred from respiration to build up fats and oils. These may be used in the cells as an energy store. They are sometimes used in the cell walls to make them stronger. In addition, plants often use fats or oils as an energy store in their seeds. Seeds provide food for the new plant to respire as it germinates. Some algal cells are also very rich in oils. They are even being considered as a possible source of biofuels for the future.

Question 3

Amino acids

Answer 3

Plants combine sugars with nitrate ions and other mineral ions from the soil. These amino acids are then built up into proteins to be used in the plant cells in many ways, including as enzymes. This uses energy from respiration.

Question 4

Starch

Answer 4

Glucose is soluble in water so if stored in plant cells it can affect the osmosis of water throughout the plant and unbalance it - starch isn’t soluble, so lots of it can be stored in the plant cells, providing an energy store for when it’s dark or light levels are low. It’s also kept in special storage areas of plants, for example, many plants produce tubers and bulbs that are full of stored starch, to help them survive through the winter. Humans often take advantage of these starch stores, found as vegetables such as potatoes and onions.

Question 5

Cellulose

Answer 5

Strengthens cell walls.

Question 6

Carbon dioxide. CO2

Answer 6

From the air, enter through the stomata on the underside of leaves through diffusion.

Question 7

Water. H2O

Answer 7

Enters through the roots which are in the soil, uses osmosis to travel up the xylem along the transpiration stream.

Question 8

Oxygen. O2

Answer 8

Used in the plant for respiration, exits into the air through stomata on the underside of the leaves.

Question 9

Glucose

Answer 9

A simple sugar.

C6 H12 O6

Question 10

Leaf adaptations

Answer 10

• Most leaves are broad, giving them a big surface area for light to fall on.
• Most leaves are thin so diffusion distances for the gases are short.
• Contain chlorophyll in the chloroplasts to absorb light.
• They have veins, which bring plenty of water in the xylem to the cells of the leaves and remove the products of photosynthesis in the phloem.
• They have air spaces that allow carbon dioxide to get to the cells, and oxygen to leave by diffusion.
• They have guard cells that open and close the stomata to regulate gas exchange.
• The waxy cuticle helps prevent water loss by evaporation.