Biology B2 revision

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  • Created by: James
  • Created on: 07-01-13 15:04


Microbes include: Bacteria, Fungi and unicellular algae. Bacteria reproduce asexually by dividing into two. Bacteria is thought to be the earliest form of life.

Yeasts are fungi. Yeasts reproduce asexually by budding

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Animal cells have:

  • Nuclei, (To regulate cell activity)
  • Cell membranes, (to protect the cell interior by only allowing certain substances in)
  • and cytoplasm. (to fill the cell and hold organelles in place)

Plant Cells have:

  • Nuclei, (To regualte cell activity)
  • Cell walls, (to support the cell, giving it it's structure)
  • Cell membranes, (to protect the cell interior by only allowing certain substances in)
  • Vacuoles, (to contain waste products and to isolate harmful materials)
  • Chloroplasts, (to contain chloropyll, so photosynthesis is possible)
  • and cytoplasm. (to fill the cell and hold organelles in place)
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Viruses are smaller than bacteria. Viruses can only reproduce in a host cell. the release of new viruses results in the destruction of the host cell and the new viruses can now attack new cells.

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Proteins and enzymes

different proteins are made of different amino acids linked together to form a chain which is then folded to form a specific shape. Prorteins have a number pf important functions e.g. enzymes, hormones and muscle tissue. The specific shape of an enzyme enables it to function. The active site of an enzyme depends on shape which is held by chemical bonds. chemical reactions are controlled by enzymes. Enzymes are proteins made by living cells. Enzymes act as catalysts for chemical reactions in the body. Enzymes have specific optimum pH and temperature. Too high pH or temperature denatures the enzyme, making it loose it's shape, so it can't catalyse reactions.

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Enzymes in washing powder

The use of enzymes enables lower temperatures to be used which requires less energy in washing. Example, Egg yolk on cloth.

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DNA is made of two long chains forming a double helix shape. Each chain is made of alternating sugar and phosphate molecules connected by bases. There are four bases, A, T, C, and G. It is the order of these bases which forms a code. This code determines the order in which different amino acids are linked together to form different proteins.

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Cell division

Cell division by mitosis enables organisms to grow, replace worn out cells and repair damaged tissues. The chromasome number remains constant and the genetic composition of the daughter cell is identical to the mother cell. Cell division by meiosis halves the chromasome number for the formation of gametes (sex cells). Each mitotic division produces two cells that are gentically identical and have the same number of chromasomes as the mother cell. Each meiotic division produces four cells that are genetically different and have half the number of chromasomes as the mother cell.

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Growth in animals and plants

Plants and animals have different patterns of growth and development and consider the advantages and disadvantages. Animals tend to grow to a finite size, whereas plants do not. Animals have a compact growth form whereas plants have a spreading, branched growth form.

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Stem cells

In mature tissues cells have generally lost the ability to differentiate into different types of cells. There are some cells, both plant and animal, that do not lose this ability and these are called stem cells. These adult stem cells retain the ability to differentiate into some different types of cells and therefore have potential for replacing damaged tissue, as do embryonic stem cells. Plants have stem cells in their shoot and root tips which retain their ability to diffferentiate into other cells throught the life of the plant.

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Diffusion is the movement of substances down a concentration gradient. A way to show this is with a visking tubing model of the gut. Diffusion does not require energy and only certain substances pass through the cell membrane in this way, most importatly oxygen and carbon dioxide. In the cell membrane, the pour size is large enough to allow small molecules through, such as oxygen, but not larger molecules such as glucose.

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Osmosis and active transport

Osmosis is the diffusion of water through a selectively permeable membrane, from the region of high water concentration to low water concentration. Active transport is an energy requiring process whereby substances can enter cells against a concentration gradient.

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What plants require

Plants require sunlight, carbon dioxide, and water to photosynthesise to generate glucose to suplly the energy needed to survive.

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Limiting factors

Limiting factors in photosynthesis in plants are:

  • Light intensity
  • Carbon dioxide concentration
  • Temperature
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Tests in leaves

Different tests that can be performed on leaves are:

  • sodium hydroxide to absorb carbon dioxide
  • soaking a leaf in hot water, then denaturing in ethanol, then pouring excess of starch on.
  • Putting a plant in a sealed container then measuring air compostion over time in a variety of conditions.
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Green plants use chlorophyll to absorb light energy and convert carbon dioxide and water into glucose, producing oxygen as a bi-product. The chemical reactions of photosynthesis within the cell are controlled by enzymes. 

Carbon dioxide + water + Light energy ----> Glucose + oxygen + water

Glucose produced in photosynthesis may be respired to provide energy, converted to starch for storage or used to make cellulose and proteins which make up the body of plants.

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Aerobic respiration

All cells require a constant supply of energy to carry out cell processes and so enable organs and systems to function. Energy is released in cells by respiration. Aerobic respiration occurs in cells when oxygen is available. During aerobic respiration (which is a series of chemical reactions within the cells controlled by enzymes) glucose and oxygen are used, energy is released and carbon dioxide and water are produced. Some energy is lost as heat.

Glucose + Oxygen ---> Carbon dioxide + water + energy

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Anaerobic respiration

In the absence of oxygen, anaerobic respiration may occur. This is less efficient than aerobic respiration. In humans energy is released from glucose and lactic acid is produced. An oxygen debt may occur. In yeast, energy is released from glucose and ethanol and carbon dioxide are produced. 

Human anaerobic respiration:

Glucose --> Lactic acid + energy

Yeast fermentation:

Glucose --> Ethanol + carbon dioxide + energy

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Digestion 1

During digestion, larger molecules must be broken down into smaller molecules to allow for them to be absorbed through the selectively permeable membranes of the cells in the intestines. In digestion, enzymes such as lypase and protease break down molecules into smaller molecules. If these enzymes are exposed to temperatures or pH levels that are too high, they denature, and can no longer break down the molecules. Visking tubing can be used as a model gut, to show how soluble substances (small molecules) can be absorbed through the wall of the small intestine and eventually into the bloodstream. 

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Digestion 2

Fats, made up of fatty acids and glycerol, proteins, made up of amino acids, and starch, made up of a chain of glucose molecules, in our food are insolube (Large molecules). They are broken down during digestion into soluble substances (Small molecules) so that they can be absorbed. You can test for the presence of starch using iodene. If the iodene turns bluey black, starch is present. The pancreas secretes digestive enzymes into the duodenum (first part of the small intesting) and secretes bile into the duodenum to help neutralise stomach acids entering the intestine.

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DO NOT USE THE PHRASE 'Air sac' IT IS AN 'Alveolus'!!!

inspired air = 21% oxygen, 0.033% carbon dioxide, 78% Nitrogen.

Expired air= 14% oxygen, 4.4% carbon dioxide, 78% nitrogen.

Mucus and cilia move dust and foreign materials up and out of the throught. Cilia are small hairs in the throught.

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