Harvesting the Sun
Plants capture the energy from the sunlight.
Plants use the energy from the sunlight to build up carbon dioxide and water into organic compounds such as glucose. This is the process of PHOTOSYNTHESIS.
Living things that make their own food are called AUTOTROPHS. Most of the autotrophs are plants, but there are some bacteria which also make their own food chemicals.
Most living things cannot make their own food, so they need to take in organic molecules, organisms that rely on other living things for food are called HETETOTROPHS.
Carbon and Nitrogen are always being recycled in the ecosystem, when an animal or plant dies its organic compounds are broken down by decay.
Some of the energy released by respirtation is trasferred to the enviroment. This energy warms up the air or water around the plants and animals and eventually radiates it back to space.
Trapping Light Energy
Less that one billionth of the Sun's energy reaches the plants on the earth, the Sun's energy output is enormous.
The equation for PHOTOSYNTHESIS
Carbon Dioxide + Water ==> Glucose + Oxygen
A glucose molecule is made up of carbon, hydrogen and oxygen atoms so glucose is a CARBOHYDRATE.
Photosynthesis takes place in CHLOROPLASTS. They contain a green pigment called chlorophyll, this absorbs light and uses the energy to start photosynthesis.
The Process of Photosynthesis
1.) The light energy splits the water into molecules into hydrogen and oxygen atoms.
2.) The hydrogen is combined with carbon dioxide from the air to make glucose.
3.) Oxygen is released as waste product.
4.) It passes out of the plant and into the air.
5.) Given enough raw materials, ligh and the right temperature, ( a large tree can make 2000kg of glucose in a day)
Why are Plants Green?
Most leaves are green because of the chlorophyll in plant cells:
Chlorophyll absorbs energy from visible light, visible light is part of the electro magnetic spectrum.
Chlorophyll absorbs red and blue light. Green light is not absorbed it is reflected by the chlorophyll.
Using Glucose from Photosynthesis
Glucose made during photosynthesis is used by plant cells in three ways.
1) Making other chemicals nedded for cell growth:
Glucose has to be converted into other chemicals needed for cells growth.
Cells need other carbohydrates as well as fats and protein, two important carbohydrates in plants are CELLULOSE and STARTCH.
Both of these large molecules made up of thousands of glucose molecules linked together.
Larger molecules made of smaller molecules are called POLYMERS. So cellulose and startch are both polymers and glucose.
Using Glucose from Photosynthesis
2.) Storing Energy in startch molecules:
Extra Glucose that is produced in a plant is converted into starch, Starch is a storage molecule. It may be stored in leaf cells.
3.) Releasing energy in respiration.
Plant cells use glucose in respirtation, the molecules are broken down, releasing the energy stored in the molecules..the equation for repiration:-
Glucose+Oxygen ==> Carbon Dioxide+Water
This energy is used to power chemical reactions in the cells, such as converting glucose to cellulose, starch or proteins.
Making Proteins needs Nitrogen
Proteins are long chains of amino acids. Every amino acid contains atoms of carbon, hydrogen, oxygen and atleast one nitrogen atom.
To make amino acids nitrogen must be combined with carbon, hydrogen and oxygen atoms from glucose.
Most of the earth's nitrogen is in the air, but plants mainly take in the nitrogen from the soil as nitrate ions. The nitrate ions are absorbed by the plant roots.
Nitrates are not the only minereals that plants need, eg. they need magnesuim to make chlorophyll, and phosphates to make DNA.
They take in nitrogen in the largest quantities because proteins are used to build cells and to make enzymes.
Nitrate ions are absorbed by active transport.
Nitrate ions are at a higher concentration inside root cells that outside, this means that the cells will move by diffusion out of the cell, not into it, to move the nitrate ions into the root cells active transport is needed.
Why is glucose stored as a starch?
Glucose is a soluable carbohydrate, cell cytoplasm is mainly waterso the glucose is dissolved.
If the concentration of the glucose is too high, then too much water moves in to the cell. This happens by osmosis. So glucose cannot be stored in cells because the osmotic balance is unequal.
The Rate of Photosynthesis
All reactions speed up when the temperture rises at 26 degrees is the optimum temperature for photosynthesis to take place in plants.
Faster Photosynthesis - Light
- At low light intensities, increasing the amount of light increases the rate of photosynthesis.
- At a certain point increasing the amount of light stops having an effect on rate of photosynthesis.
Why does the rate not keep on rising?
Photosynthesis needs more than just light energy.
Extra ligh makes no difference to the rate of photosynthesis if the plant does not have carbon dioxide, water or chlorophyll to use the energy to the full.
Light intensity stops having an effect on the rate of photosynthesis because one of the other factors is short in supply, the factor is called LIMITING FACTOR.
Balancing respirtation and photosynthesis
Carbon Dioxide is taken out of the atmosphere by photsynthesism, the carbon is used to produce glucose molecules. The glucose is broken down during repiration. This released carbon dioxide back into the atmosphere.
Plants only carry out photosynthesis when they are in the light, however respiration happens 24 hours.
-Plant take in carbon dioxide for photosynthesis during the day.
- They make carbon dioxide in repiration 24 hours a day.
- During photosynthesis they take in more carbon dioxide for photosynthesis than they make in respiratiion.
When photosynthesis and respiration are taking place at the same rate, glucose production and use in the plant are balanced. This is called a plant's COMPENSATION POINT.
Food chains start with AUTOTROPHS. These are the producers which use carbon dioxide to make organic chemicals. These chemicals pass to the HETERTROPHS.
First herbivores eat the producers and then the herbivores are eaten by the carnivores.