Cards on B2 - Revision 



Light Microscope - uses the power of lenses and light to enlarge what is being viewed. 10x or 15x magnification. Used for studying plant cells, bacteria and human/animal cells.

Laser Imaging Microscope - produces 3D images of the cell contents. Used to examine live cells, investigating diseases, cell development and neuroscience. 

Electron Microscope - most powerful microscope. Uses electrons to create an image of the specimen but it can only be used with dead tissue. 

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A microbe is a microscopic living organism. The most important groups of microbes are bacteria, fungi, algae and viruses. 

Bacteria - A single bacterium is very small. All bacteria have a cytoplasm, a thin cell membrane and a cell wall. They reporoduce asexually by dividing into two. Some bacteria cause diseases such as TB. 

Fungi - Yeats, mushrooms and moulds are fungi. They are larger than bacteria. They have a nucleus, cytoplasm and a membrane surrounded by a cell wall. They reproduce asexually. 

Algae - A simple many celled organism which do not have roots, stems or leaves. They live mainly in water and feed by photosynthesis. 

Viruses - They are much smaller than bacteria. They consist of a protein coat surrounding a small number of genes and can only reproduce inside a living host cell. 

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Stem Cells

These are unspecialised, undifferentiated cells which can change and divide to produce any of the 300 different types of cells that make up the human body. 

They could potentially be used to repair and replace damaged human tissue. In the FUTURE, they are hoped to be used to treat and cure diseases and injuries including Parkinsons' disease and strokes. 

They can be taken from unused human embryos or from the patient themselves. They can only be taken from human embryos if consent has been given (raises ethical issues). Plant also have stem cells which are found in their shoot and root tips (meristem). 

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Diffusion, Osmosis & Active Transport

Diffusion - is the movement of a liquid or gas due to random collisions between particles. Particles move from an area of high concentration to an area of low concentration. This is known as a concentration gradient. Diffusion uses very little energy and only certain substances pass through the membrane by this method.

Osmosis - is the diffusion of water through a selectively permeable membrane, from an area of high water concentration to an area of low water concentration.

Active Transport - uses energy to transport substances into cells against a concentration gradient. 

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Mitosis & Meiosis

Mitosis - the type of cell division that results in growth. The number of chromosomes in each new cell remains constant and the genetic composition of the daughter cells is identical to the mother cell. See Booklet

Meiosis - the type of cell division only takes place to form sex cells. The number of chromosomes is halved and the genetic compostition of the daughter cells is not identical to the original cell. See Booklet

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Growth Patterns in Plants & Animals


  • Growth occurs in restricted areas only
  • Growth pattern is for access to resources e.g. light, water & minerals
  • Spreading, branched and static growth pattern


  • Compact and finite growth for movement to obtain food
  • Growth occurs throughout the body
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Structure of DNA

DNA is made up of two long chains of alternating sugar and phosphate molecules connected by bases and that this structure is twisted to form a double helix. 

Within the nucleus of every cell are tiny structures called chromosomes. There are 46 chromosomes in human cells. Each chromosome is made of tightly coiled DNA. The DNA molecule has a double helix structure. The chemical bases in the helic make up the genes. There are four bases A, T, C and G (C-G, A-T, C-G, A-T). It is the order of these bases which forms a code. 

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During photosynthesis green plants use light energy to join carbin dioxide and water to form glucose. Oxygen is a by-product of photosynthesis. The green pigment chlorophyll absorbs the light for photosynthesis.

Carbon Dioxide + Water ----> Glucose + Oxygen

The rate of photosynthesis is affected by temperature, concentraion of carbon dioxide and light intensity. light intensity & carbon dioxide concentration would produce the same graphs yet temperature would not

Uses of the products of photosynthesis (CROPS)

Used as a raw material to make Cellulose, Oils and Proteins, which make up the body of plants. It may be Respired to provide energy. Turned into Starch for storage. 

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Digestion & Enzymes

The Alimentary Canal See additional sheet

The Purpose - Fats, Proteins and Starch in our food are insoluble and need to be digested into soluble substances so that they can be absorbed into the bloodstream. 

Food moves through the digestive system by the process peristalsis. 

Classes of Enzymes - 

Carbohydrase - Carbohydrates - Sugar

Protease - Proteins - Amino Acids

Lipase - Fat - Glycerol & Fatty Acids

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Digestion & Enzymes (Part 2)

Lock & Key Theory - 

Each enzyme has it's own substrate which will only fit into the enzymes active site. Extremes of pH and temperature would cause the enzyme to denature (shape of active site would change) meaning the enzyme activity will be slower. If the temperature is lower than 37 degrees the rate of reaction would decrease. 37 degrees is the optimum temperature. 

Enzymes released See additional sheett

The action of Bile - to emulsify fats. To increase the surface area increasing the efficency of the lipase enzymes. To neutralise the acids from the stomach to allow the enzymes to work in the small intestine.

Uses of digested foods See additional sheet 

The Large Intestine - Any food which is not digesteed and absorbed into the blood enters the large intestine. Here, water is removed to form solid faeces. After time these pass out of the anus due to peristalsis.

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The Human Respiratory System

Diagram - see booklet

Inspiration and expiration depend upon changes in the pressure and volume of the thorax. Movements of the diaphragm and rob cage bring about these changes. 

Table - see additional sheet

The composition of inspired and expired air - see booklet

Air contains a mixture of gases. When we breathe air into the lungs, oxygen passes into the blood and is absorbed by the red blood cells. At the same time, carbon dioxide and water vapour pass out of the blood and into the lungs to be breathed out. This is called gaseous exchange. See booklet

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Aerobic & Anaerobic Respiration

Aerobic - 

Glucose + Oxygen ---- Carbon Dioxide + Water + Energy

Anaerobic - 

This does not release as much energy as aerobic.

Glucose ---- Lactic Acid + Energy

An oxygen debt builds up during exercise, which must be repaid when exercise stops. 

Lactic Acid + Oxygen ---- Carbon Dioxide + Water

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