B4

Movement

Respiration

Sensitivity 

Growth

Reproduction

Excrection

Nutrition

What are Enzymes?

Enzymes are proteins. They are biological catalysts - they speed up reactions. The chemical reactions that take place in cells rely on enzymes. They speed up reactions 10 billion times.Without enzymes, reactions will take place too slowly.

How to Enzymes work?

Enzymes work by attaching to a substate, and braeking it down into smaller units. It does this at the active site.

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How does temperature affect Enzymes?

Due to the fact that enzymes are proteins, they work best at a certain temeperature. When the temperature is too high, the shape of the enzyme permanentley changes meaning that the enzyme can no longer react with other molecules. The enzyme has denatured.

The temparature at which anenzyme works best is called its optimum temperature. Enzymes in humans work best at 37 degrees. Some organisms have cells and enzymes adapted to dfferent temperatures.

pH aslo affects Enzymes

Proteins including enzymes can be damaged by acids and alkalis. The shape of an enzyme's actiive site will be changed if bonds holding the protein chains together are broken. The substrate will no longer be able to fit, the enzyme becomes denatured. Every enzyme has an optimim pH at which it works best,

During photosynthesis, Plants trap energy from sunlight and use it to make all the molecules they need for growth. These include sugars, starch, enzymes and chlorophyll. These molecules feed other organisms.along the food chain. So photosynthesis supplies food for life on Earth.

(6) CARBON DIOXIDE + (6) WATER --------(light energy)--------> GLUCOSE + (6) OXYGEN

 A glucose molecule is made of carbon, hydrogen abd oxygen atoms, making it a carbohydrate.

Photosynthesis takes place in the chloroplasts. They contain a green pigment called chlorophyll. Chlorophyll absorbs light and uses the energy to kick-start photosynthesis.

Energy from light splits water molecules into hydrgen and oxygen atoms. The hydrogen is combined with carbon dioxde from the air to make glucose. The oxygen is released as a waste product. It passes out of the plant into the air. Given wnough raw materials, light, and the right temperature, a large tree can make 2000kg of glucose in a day.

Glucose and oxygen are made by photosynthesis. Glucose can be converted into starch for storage or cellulose to make new cell walls. Glucose can also be built up into other molecules such as fats, protein and chlorophyll.

(1) Making other chemicals needed for cell growth: Glucose is converted into other carbohydrates, as well as fats and proteins. Two important carbohydrates in plants are cellulose and starch. Cellulose and starch are both polymers of glucose. They are made up of thousnads of glucose molecules linked together.

(2) Storing energy in starch molecules: Any excess glucose is converted into starch. Starch is a storage molecule. Starch can be converted back to glucose when needed. Starch is stored in leaf cells, but some plants have special organs, such as the tubers of a potato, which have cells that are filed with starch.

(3) Releasing energy in respiration: Glucose molecules are broken down by respiration, releasing the energy stored in the molecules. This energy is used to power chemical reactions in the cells, such as converting glucose to cellulose, starch or proteins.

Diffusion is when molecules move from areas of higher concentration to lower concentration.

Diffusuion is affective by:

• Temperature
• Size of Molecules
• Steepness of Concentration Gradient

Diffustion is a PASSIVE MOVEMENT meaning it does not require energy to occur.

Speed of Diffusion:

Osmosis is the movement of water molecules from a region of HIGH WATER COMCENTRATION to a region of LOW WATER CONCENTRATION across an semi permeable membrane.

OSMOSIS

Osmosis is a special example of diffusion. It is the diffusion of a substance through a semipermeable membrane from a more dilute solution to a more concentrated solution. This process is also passive since no external energy is needed.

A semipermeable membrane is a barrier that permits the passage of some substances but not others. Cell membranes are described as selectively permeable because not only do they allow the passage of water but also allow the passage of certain solutes (dissolved substances).

Some major examples of osmosis:

1. Absorption of water by plant roots.
2. Reabsorption of water by the proximal and distal convoluted tubules of the nephron.
3. Reabsorption of tissue fluid into the venule ends of the blood capillaries.
4. Absorption of water by the alimentary canal — stomach, small intestine and the colon.