B2 2.1

Carbon dioxide + water (+ light energy) ---> Glucose + Oxygen

During photosynthesis, light energy is absorbed by the chlorophyll in the chloroplasts. Energy is used to convert carbon dioxide from the air and water from the soil into glucose.

Using iodine we can test for starch because it turns a dark blue colour if starch is present.

Leaf adaptations- Leaves have a big surface area for light to fall on, contain chlorophyll to absorb light energy, they have air spaces to allow carbon dioxide by diffusion, they have veins which bring water to the cells.

Limiting factors- When something is in short supply and can limit the amount of photosynthesis in a plant.

Light- Light is needed for energy and photosynthesis will stop without it.

Temperature- Photosynthesis is controlled by enzymes so when the temperature is too high they denature therefore stop working quickly.

Carbon dioxide levels- Plants need it to make glucose so if there is very little then it can limit the rate of photosynthesis. There is more carbon dioxide at night but it can't be used up because there is no sun therefore in the morning it gets all used up.

Glucose is broken down using oxygen to provide energy for the cells. This leaves carbon dioxide and water as waste products. This energy is used to build up smaller molecules into bigger molecules.

Plants and algae also build up glucose into cellulose which is used to strengthen cell walls.

Plants use some of the glucose to make amino acids. They combine sugars with nitrate ions and mineral ions from the soil. The amino acids are built up into proteins to be used in the cells.

Some glucose is changed into starch for storage. Glucose is soluble in water so if lots of glucose was stored in plant cells it could affect the water balance of the whole plant. Starch is insouble so it will have no effect on water balance.

Many plants produce tubers and bulbs which are full of stored starch to help the survive through the winter.

The more a plant photosynthesises, the more biomass it makes and the faster it grows.

Garden Greenhouse- It is much more controllable than outside and the atmosphere is warmer. This speeds up photosynthesis so plants flower and fruit earliar and produce higher yields. We can also use them to grow fruits we can't usually grown in the UK.

Hyrdoponics- Growing plants in water enriched by mineral ions rather than soil.

Commercial greenhouses control the limiting factors so they can get the quickest possible rates of photosynthesis. They control greenhouses using computer software that is expensive however turnover is fast so high profits.

Factors affecting living organisms:

Temperature- If plants can't grow then less herbivores will survive.

Amount of light- It changes the distribution of plants and animals because of different needs for photosynthesis. The breeding cycles of many animal and plant species are linked to the day length.

Availability of water

Availability of oxygen and carbon dioxide- Some invertebrates can survive in water with very low oxygen levels however most fish need. Carbon dioxide levels are a limiting factor of photosynthesis. They can also affect the distribution of organisms. E.g. mosquitoes are attracted to the animals on whose blood they feed by high carbon dioxide levels.

Quadrats- A quadrat is a square frame that you lay on the ground to give you the outlines of your sample area. You must choose sample areas at random so you get a true reflection of the distribution of the organisms. You take a random number of readings then find the mean number of organisms per m². This is known as quantitative sampling which we use to compare the distribution of the same organism in different habitats.

Transect- The most commonly used transect is a line transect. They aren't random. You stretch a tape between two points and then sample along that line in regular intervals using a quadrat. You can also measure some physical factors. E.g. Light levels, soil pH.

Reproducible- Other people can do the investigation and get similar results.

Valid- You must be answering the question you are asking.

Control variables- It isn't possible to control variables of the natural environment but you can control what time of day you measure at.