How do plants make their own food? All they need are very simple substances and some energy. They use the substances produced to grow and to increase in mass.

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The leave is the organ where the plant makes food. This process is called photosynthesis.Photosynthesis uses light energy from the sun to combine water with carbon dioxide. The products are oxygen and glucose (a type of sugar). Glucose is used by the plant to make every other substances the plant needs.

The word equation for photosynthesis is: water + carbon dioxide-------glucouse + energy.


Glucose is used by the plant as a supply of energy.The glucose is made into sucrose to carry away from leaf. It can be stored as starch for later use or converted into other chemiclas like celloluse for the cell walls. Some of this cellulose is combined with minerals to make proteins needed for growth. Fats and oils found in the seeds are also made from glucose.


external image agua.jpgWater is needed for life. Without water you feel thirsty and need a drink. You swallow the water absorbed into your blood from the digestive system. The water can then moved to the tissue where it is needed and your thirst disappears.


The water is absorbed from the soil by the roots. Then it must move through the plan into the stem and leaves to get to all the cells needing the water. If the plant becomes short of water it wilts and may die.


Water move from the solid into the roots hair by osmosis (the movement of water from an area of high water concentration to an area of lower water concentration). The water will continue to move through the root cells, from cell to cell, until it reaches the xylem vessels. Water is used for photosyntesis, supporting the cells or it just evaporates and diffuses. The evaporation of water into the air means there is less water in the leaf cells and xylem vessels. Water movement replaces the lost water. This movement is called transpiration. wilting-transpiration-stream.jpeg Osmosis.jpg


Not just plants need water to live. Water is essential for both plants and animals.

Our body is about 70% water. 2,5 litres are found in the blood so most is sorrounding the cells as tissue fluid or in the cytoplasm of the cells.

The water is important for four reasons:

  1. As a solvent, to let all the other chemical dissolved.

  2. As part of chemical reaction

  3. As a coolant. The water forms part of sweat relased out by the skin and then it evaporetes , so it takes away heat.

  4. To transport substances around the body.


Water moves into both plants and animals by osmosis but the nutrients enter equal?

The nutrient for a plant must come from the soil and are absorbed along with water.This are called mineral salts.The plants need them in small amounts.

A mineral salts is soluble in water and the mineral particles can move about.There will always move where there are more of them to where there are less.This movement is called diffusion.

Diffusion is the movement of particles from an area of high concentartion to an area of lower concentration due to the random motion of particles.

The root hair cells use energy to absorb the mineral salt particles from the soil into the root.The selective membrane makes sure that the minerla salt cannot leave the ceel to return to the soil.This proceess of usin energy to absorb nutrients is called active transport.

Active transport is the movement of particles against the concentration gradient, through cell membrane.



Food contains energy and chemicals that are needed by animals.The energy originally comes from the plants. Humans can then eat the plants to get the energy or they can eat other animals that have eaten plants. There is a an amazing range of food that humans eat .They can be grouped in different ways.There are seven nutrient groups; carbohydrates, fats, proteins vitamins, minerals, fibre and water. This information is listed bellow:


There are two types of carbohydrates:

Simple carbohydrates(sugars) are sweet and dissolve easily.

Complex carbohydrates are large molecules made of glucose.They are not sweet and they are used to store energy. Common carbohydrates can be found in potatoes and bread.


They are large molecules made up from chains of amino acids

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- Essential amino acids: These amino acids cannot be made by our bodies, animal products like meat have more essential amino acids than plant products such as beans.

- Non- essential amino acids

These proteins are used by the cells for growth and repair. Proteins can also be used for energy, if the body is starving and no carbohydrates or fat is available they are broken down into carbon dioxide, water and urea.



There are four types:

1) Calcium: It is needed for the structure of bones and teeth.

Lack of calcium causes rickets.

2) Iron: For carrying oxygen in red blood cells.

The lack of iron can cause Anemia.

3) Phosphorous: It is needed for energy release.

4) Potassium: It helps chemical reactions in cells.

A deficiency of mineral salts causes a deficiency disease


The majority of this group of chemicals cannot be made by our body, they must be eaten in our food. Without enough of each vitamin, deficiency diseases may occur.

Lack of vitamin C, is called scurvy. Vitamin C is called ascorbic acid. None of the vitamins provides energy.

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These are substances that the body cannot digest. Fibre helps the movements of all the other substances along the canal. The fibre encouranges the right types of bacteria to grow in the large intestine so that fewer poisions are produced from harmful bacterias.

A large amount of fibre comes from plant cell walls.It is very important a balance diet to prevent diarrhoea or constipation and cancer of the colon.


1) Water disolves most of the other chemicals in our body and allows chemical reactions.

2) The water tranports the substances around the body.

3) Some reactions need water as a raw material.

4) Water is used to cool the body. It is lost by the evaporation of sweat.

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These also contain carbon, hydrogen and oxygen but there is a very little oxygen compared to the amount of hydrogen. Fats do not dissolve in water and so have to be carried in the blood in a special way. They are combined with proteins, fats give out twice as much energy as carbohydrates. Fats are made from two different parts-- fatty acids and glycerol.


A balanced diet has all of the nutrients required by the body. Any diet that causes any health problem causes malnourishment.

People who take in too much energy, by eating either too much carbohydrate or fat, will become obese. The extra weight carried by the body means the heart must pump blood to more tissues.

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Obese people are more likely to suffer a heart attack or external image cirugia-sistema-circulatorio-arteria-grasa-obesidad-secuelas.jpgdifferent disease, in the picture we can see a person with obesity problems.

Too little food causes tiredness and wasting diseases which are most common in developing countries. Eating most of the carbohydrate you need as sugar is bad for your teeth.


If there is too much fat in the diet some is left in the bloood vessels as it travels around. This narrows the vessels and causes a strain on the heart. The fatty deposit can trigger( produce) the formation of blood clots which can block or narrow the vessels. If a blood clot is formed and it gets stuck in the brain, it causes a stroke. If it gets stuck in a blood vessel feeding the heart muscle with oxygen then a heart attack can occur. Food for humans comes from plants or other animals. The food is made from large molecules which cannot be absorbed into the blood. They must be broken down, absorbed and then changed into the form needed by our own bodies. .

The organ system that has the job of taking in food and making it available for the rest of the body is the digestive system. It is a long tube running throught the body from the mouth to the anus. Special substances called enzymes are released to break down the food. This process is called digestion. The digested food is then absorbed into the blood stream. Any food that cannot be digested is passed out of the anus, by a process called egestion. The digestive system consists of many organs, each especialised for one function. The food passes throught the organs in sequence so that it can be progressively broken down and then absorbd.


Ingestion is the act of taking food into the mouth. It is chewed to break it down into smaller pieces and to mix in with saliva. The smaller pieces are easier to swallow and have a bigger surface area for enzymes to break down the food.

The saliva contains mucus which helps to lubricate the food. It also contains an enzyme an enzyme which breaks down starch into simple sugar molecules. Enzymes are special substances that speed up chemical reactions. They are proteins and each enzyme has very specific shape.

This special shape means that a substrate molecules can fit into the enzyme and be broken down in digestion. Enzymes are useful in digestion because they help to break down the food. The enzyme in your saliva is called amylase and it starts work on digesting food in your mouth.

Teeth are also important. Humans have two set sets of teeth. When young, the jawgrowths but the teeth cannot. The second set is larger than the first and there are 12 more teeth in total. If you look after your teeth this makes sure you can chew your food forall your life. The food is pushed down the oesophagus. external image tooth-internal-structure.jpegdigestive_system.gif


Food has been salowed entres to the stomach.The average time for food to stay in the stomach is about four hours.The churning of the stomach helps to physically break up of foood and to mix it with the gastric juice produced by gland in the walls. The juice us mainly hydrocloric acid which kills most micro-organism in the food.An enzyme breaks down proteins into smaller molecules. The acid mush is released from the stomach in to the small intestinein small amounts.In the small intestine many differnet enzyme are used to break down the large molecules in food. We can name three ones

  1. Lipases-break down fats

  1. Carbohydrases-break down carbohydrates.

  1. Proteases-digest protein.

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The small intestine has a massive surface area for absorption of the digested food molecues. The surface area is increased by the following:

-It is long

-The absorbing surface is folded so there is a larger surface.

-On the folds are vili wich stick up from the surface like many fingers

-Each villnius has tiny projections called microvilli

The soluble food is absorbed into the blood by diffusion. The blood goes to the liver and any poisons that have been absorbed with the digested food can be destroyed.

Most water is absorbed into the blood. Some of the bacteria in the large intestine can use the remains of the food to make some vitamins the body needs. These are absorbed with the water. Food needs the fibre to help it to move throught the large intestine. The feaces stored in the last part of the large intestine and must removed(egestion). Egestion means getting rid of undigested food that has not absorbed into the cells of the body.

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This photographs shows the intestaines, containig villi.