• Created by: Emma
  • Created on: 15-05-11 13:21


Plants need food to have enough energy for photosynethesis, respiration, reproduction and growth. Although, plants do not need to eat as they make their own food!, they do it by photosynethis. The equation for photosynethesis is:


The cells in the leaves are full of small green parts called chloroplasts. They contain green substance called chlorophyll.

Some of the glucose that is produced is used imediatly by the cells of the plant although a lot of the glucose made is converted into starch for storage.

Iodine soloution is yellowy-brown liquid which turns DARK BLUE when it reacts with starch. You can use IODINE TEST FOR STARCH to show that photosynthesis has taken place in the plant.

The leaves of plants are perfectly adapated because:

  • Most leaves are broad, they have a big surface area for light to fall on,
  • They contain chlorophyll in the chloroplasts to absorb the light energy
  • They have air spaces which allow carbon dioxide to get to the cells and oxygen to leave them
  • They have veins, which brings plenty of water to the cells of the leaves.
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Limiting Factors

Plants grow better in the summer compared to them growing in the winter, this is because plants need light, warmth and carbon dioxide if they are going to photosynthesis as fast as they can. If any of these things are in short supply they may limit amount of photsynthesis a plant can manage. This is why they are known as limiting factors.

Light -  This is the most obvious factor affecting the rate of photosnythesis, if there is plenty of light lots of photosynthesis can take place unlike if there was not enought light (LIGHT AFFECTS RATE OF PHOTOSYNTHESIS)

Temperture - Temperture affecrs all chemical reactions. As the temperture rises so will the rate of photosynthesis. Although it is controlled by enzymes as it is a living organism and the enzymes will be destroyed as the temperture rises to about 40 to 50 degrees. This means that if the temperture gets too high, the rate of photosynthesis will fall as the enzymes controlling it are denatured.

Carbon dioxide levels - Plant need carbon dioxide to make GLUCOSE. Increasing the carbon dioxide levels will increase the rate of reaction.

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How plants use glucose

Respiation -  Any other living cells repire all the time, They break down glucose using oxygen to provide energy for their cells. Carbon dioxide and water are the waste products of the reaction. The energy released in respiration is then used to build up smaller molecules into bigger molecules. Plants also build up sugars into more complex carbohydrates like celluose. They use this to make new plant cell walls. Plants use some energy from respiration to combine sugars with other nutrients (mineral ions) from soil to make amino acids. Energy from respiration is also used to build up fats and oils to make a food store in seeds.

Transport and Storage - The food is needed all over the plant, it is moved around the plant in a special transport system. There are TWO seperate transport systems in a plant. The PHLOEM is made up of living tissue, it transports sugars made by photosynthesis from the leaves to the rest of the plant (carried to ALL parts of a plant)

The XYLEM is the other transport tissue. It carries WATER and MINERAL IONS from the soil around the plant.

Glucose is SOLOUBLE(dissolves in water) & Starch is INSOLOUBLE (doesnt) 

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Why do plants need Minerals?

The problem with the products of photosynthesis is that they are all carbohydrates. Carbohydrates are very important as plants use them for energy for storage and even for structural features like cell walls.A plant needs protein to act as enzymes and to make up a large part of cytoplasm and the membranes.

Glucose and starch are made up of carbon, hydrogen and oxygen. Proteins are made up of amino acids which contain carbon, hydrogen, oxygen and nitrogen. Plants need nitrates from the soil to make protein. If the plant does not get enough nitrate it will not grow healthy as it would become small and stunted. When the plant dies the nutrients would go back into the soil for other plants to use.

Plants also need magnesium to make chlorophyll. This is vital to plants as chlorophyll absorbs the energy from light which make is possible for plants to photosynthesis , if it does not get light the plant will die. Plants only need a tiny amount of magneisum however if they dont get enough they will go pale,yellowish areas on their leaves.

If the plant does not have enough of the mineral ions the plant will die as it does not get its needs.

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Plant Problems?

Small Holder - Different crops had to be grown each year (crop rotation) and the land was rested between crops. Fields lay fallow (no crops were grown) every few years to let the land recover. Manure was the main fertiliser. By rotating it also keeps the diseases at bay. Do not earn a great deal of money

Arable Farmer - It is a pretty big area and they grow wheat and ol seed ****. They have to be careful on what they spend their money on as it also is not a big profit job.  After they have harvested he would plough the stubble back into the soil, they used to burn it although they are no longer able to do that. They are able to support their family with the income and also employs one local person.

Hydroponics Grower-  This cab limit the rate of photosyenthesis as may not always get the correct level of what the plant needs. Although, they can control what temperture etc that they need to grow faster. They do not need many employees as the computer control it all.

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Chapter Two questions ( 2.1 - 2.4)

  • What is the word equation fot Photosynthesis?
  • Why do plants not need to eat?
  • What will Iodine test for starch do?
  • How does broad shape of leaves help photosynthesis to take place?
  • Why do plants grow faster in the summer compared to the winter?
  • Why does temperture affect photosynthesis?
  • Why do plants respire?
  • What is the main storage substance in plants?
  • Is Glucouse a solouble or insolouble? and what does it mean?
  • What are the products of photsynthesis?
  • Why do plants need nitrate?
  • Why do plants need magensium?
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  • Carbon dioxide + Water (+light energy) --> Glucose + Oxygen
  • Plants dont need to eat as they produce their own food
  • A iodine test will show if photosynthesis has taken place in a plant
  • A big surface area for light to land on
  • They grow faster in the summer as they will get Light which will be speed up photosynthesis
  • Temperture does affect photosynthesis as if it is too hight the enzymes that control photosynthesis will denature
  • Plants respire because any living organism will
  • Stacrch
  • Glucose is Solouble and this means it will disolve in water
  • They are carbohydrates
  • Plants need nitrate as without it the plant will be small and stunted and will not be able to grow healthy
  • Plants need magnesium as without it the plant will not have chlorofyll which will mean that it will not absorb any energy to absorb light and the plant will die.
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nice one emmma :P x

Former Member


very helpful thanks

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