B8: Photosynthesis

What happens to the energy during photosynthesis

Energy is transferred form the environment to the chloroplasts by light. This energy is then transferred to covert C0₂ from the air + water from the soil into glucose

What type of reaction is photosynthesis and why

Endothermic: It needs an input of energy from the environment.

Word equation for photosynthesis

carbon dioxide+water→glucose+oxygen

Symbol equation for photosynthesis

6CO₂ + 6H₂O → C₆H₁₂O₆ + 6o₂

What happens to the glucose during photosynthesis

Some is used up immediately by the cells for respiration but most is converted to insoluble starch and stored

Leaf adaptations for photosynthesis

• Broad: big surface area for light to fall on

• Thin: Diffusion distances for the gases are short

• Contain chlorophyll: Absorb light

• Veins: Brin plenty of water into the xylem to the cells of the leaves

• Air spaces: Allow carbon dioxide to get into the cells and oxygen to leave by diffusion

• Guard cells: Open and close the stomata to regulate gas exchange

How is algae adapted to photosynthesis in water

• Large surface area to absorb carbon dioxide dissolved in the water around them

• The oxygen they produce also dissolves in the water around them as it is released

Where does a plant get its carbon dioxide and water from for photosynthesis

Carbon dioxide is from the air through stomata in the leaves, while water is absorbed from the soil through the roots.

What is a limiting factor

When something is in short supply and limits the amount of photosyntheses a plant can manage

What are the 4 limiting factors

• Light

• Temperature

• Carbon dioxide concentration

• Chlorophyll levels

How does light affect photosynthesis

• If there is plenty of light, lots of photosynthesis can take place

• If there’s little to none photosynthesis will stop

• Brighter light = faster rate of photosynthesis

How does temperature affect photosynthesis

• As it rises, the rate of photosynthesis increases as the reaction speeds up

• However photosynthesis is controlled by enzymes: If temp gets too high the enzymes will denature and the rate will fall

How does carbon dioxide concentration affect photosynthesis

• increasing it will increase the rate of photosynthesis

• usually its a limiting factor because there’s only 0.04% in our atmosphere

• At night carbon dioxide concentrations rise because the plant respires but doesn’t photosynthesise in the morning light and temp increase so most of the carbon dioxide is used up

How to investigate the effect of light intensity on the rate of photosynthesis (method)

• Place a piece of pondweed (Elodea) into a boiling tube filled with sodium hydroxide solution

• Position the boiling tube to be 10cm away from the light source

• Record the rumble of bubbles observed in a set time

• Repeat steps for different distances

How to improve the investigation of the effect of light intensity on the rate of photosynthesis

• Repeat the experiment at least twice for each distance and calculate a mean for more accurate results

• Use a glass tank between the lamp and plant to prevent the heating of the plant or use an LED bulb that releases very little heat energy

Variables of the light intensity rate experiment

independent - distance from light source

dependant - the number of bubbles produced per minute

control - concentration of sodium hydroxide solution, same piece of pondweed

How does chlorophyll levels affect photosynthesis

• If a plant doesn’t have enough minerals especially magnesium it cant make chlorophyll

• the rate of photosynthesis will drop and eventually the plant may die

How is glucose broken down and why

by oxygen to provide energy for the cells

What do plants use glucose for

• Complex carbohydrates such as cellulose (to strengthen their cell walls)

• Some is converted into a starch to be stored

How can glucose and starch affect the plant (in terms of water)

• Since glucose is soluble in water if ti were stored in plant cells, it could affect the way water moves in and out of the cells by osmosis

• Lots of glucose could affect the water balance of the whole plant

• starch is insoluble in water so it doesn’t have an effect on water balance so plants can store large amounts of it in their cells (its also the main source of energy)

Where is starch stored

• Cells of the leaves - it proves an energy store for when its dark or when light levels are low

• Special storage areas for example many plants produce tubers and bulbs filled with stored starch - helps them survive through winter (humans take advantage of these stores found as vegetables like potato and onion)

Why cant you just add iodine to test for starch in a plant

• Because the waterproof cuticle keeps the iodine out

• The green chlorophyll would mask any colour changes if the iodine reacted with starch

How can you test for starch in a plant

• Boil the leaves of the plant in ethanol to destroy the waxy cuticle and then to remove the colour

• Rinse in hot water to soften them

• Add the iodine

• It should turn blue black in the presence of starch

How do plants use glucose from photosynthesis to make amino acids

• They combine sugar with nitrate ions and other mineral ions from the soil

• These amino acids are then built into proteins to be used in the plant cells in many ways

What are amino acids used for in plants

• For enzymes which also uses energy from respiration

How does algae make amino acids

By taking the nitrate ions and other minerals they need from the water they live in

How are carnivorous plants (such as Venus fly traps and sundwes) adapted to live in nitrate poor soils

• They obtain most of their nutrients from the animals such as insects that they catch

• They produce enzymes to digest the insects that they trap

• They then use the nitrates and other minerals fro the digested bodies of their victims in place of the nutrients that cannot get from the bog soil

What are lipids used for in a plant

• They’re used in cell walls to make them stronger

• As an energy store in their seeds (the seeds provide food for the new plant to respire as it germinates)