Cells, Tissues and Organs

Cells, Tissues and Organs

1. Animal and Plant Cells

   • Most human cells, like most animal cells contain a nucleus, cytoplasm, cell membrane, mitochocondria and ribsomes.
   • Plant and algal cells contain everything in an animal cell, plus many also contain chloroplasts and a permanent vacuole filled with sap.
   • Plant cells are different because they have different functions
   • KEYWORDS
     • Nucleus
     • Cytoplasam
     • Cell Membrane
     • Mitochondria
     • Ribsomes
       • The site of protein synthesis in a cell
     • Protein
     • Algal Cell
       • The cell of algae, single celled or simple multicellular organisms, which can photosynthesis but it is not a plant
     • Cell Wall
       • A rigid structure which surrounds the cells of living organisms apart from animals
     • Chlorophyll
     • Vacuole

2. Specialised Cells

   • Cells are specialised to carry out a particular function, e.g. fat cells, cone cells, root hair cells and sperm cells.
   • If a cell has many ribsomes it is making a lot of protein, e.g. Gland Cells which produce enzymes.
   • Receptor cells have special structures which enable them to detect stimuli, e.g. the cone cells in the eye are light sensetive
   • Neutrons are specialised to carry impulses from receptors to the CNS
     • CNS = Centeral Nervous System
   • Plant cells with many chloroplasts will be photosynthesising, e.g. mesophyll cells of a leaf
   • Root hair cells increase the surface area of the root so that it can absorb water and mineral ions efficiently.

3. Diffusion

   • Molecules in gases and liquids move around randomly because of the energy they have
   • DIFFUSION is the spreading out of the particles of a gas, or of any substance in solution.
   • The NET MOVEMENT into or out of cells depends on the concentration of the particles on each side of the cell membrane
   • Because the particles move randomly, there will be a net (overall) movement from an area of high concentration to an area of lower concentration.
   • The difference in concentration between two areas is called the concentration gradient
   • The larger the difference in concentration, the faster the rate of diffusion

4. Tissues and Organs

   • A tissue is a group of cells with similar structure and function
   • During the development of multicellular organisms the cells differentiate
     • Multicellular Organism
       • An organism which is made up of many different cells which work together. Some of the cells are specialised for different functions in the organism
   • Animal tissues include...
     • Muscle tissue which can contract to bring about movement
     • Glandular Tissue, to produce substances such as enzymes or homones
     • Epithelial Tissue, which covers some parts of the body

5. Organisms in the Enviroment

   • Photosynthesis
     • Photosynthesis can only be carried out by green plants and algae
     • Chlorophyll in the chloroplasts absorbs the Sun's light energy.
     • The Process
       • 1. Carbon dioxide is taken in by the leaves, and water is taken up by the roots.
       • 2. The chlorophyll traps the light energy needed for photosynthesis.
       • 3. This energy is used to convert the carbon dioxide and water into glucose.
     • Oxygen is released as a by-product of photosynthesis
     • some of the glucose is converted into insoluble starch for storage.
     • Keywords
       • Light Energy
         • Energy in the form of light.
       • Glucose
         • A simple sugar.
       • Variegated
         • Having diffrent colours, e.g a green and white leaf.
     • Making the most of photosynthesis
       • Plant growers try to give their plants the best conditions for grwoth by controlling the enviroment
       • Plant grwoers can atificially control the enviroment to improve plant growth
       • It can be expensive to provide a suitable temperature, light and carbon dioxide. The grower has to compare the biomass of plants growth indoors and outdoors without these extra factors.
   • Limiting Factors
     • Plants grow best when they have enough light, carbon dioxide and water, and are kept at a suitable temperature.
       • If any of these conditions are not met, the rate of photosynthesis will be limited.
     • A lack of light will slow down the rate of photosynthesis.
     • If it is cold, then th enzymes will not work effectively and this slows down the rate of photosynthesis.
     • Anything which puts a cap on the rate of photosynthesis is a limiting factor.
     • Variables which need to be controlled are light, temperature and the type of plant being used.
     • Keywords
       • Limiting Factor
       • Indepenent variable
       • Dependent Variable
   • How Plants Use Glucose
     • Plants and algal cells produce glucose during photosynthesis
     • Glucose produced in photosynthesis can be used in a variety of ways.
     • Plants and algae need nitrate ions to make proteins.
     • Uses of soluble glucose
       • Converted into insoluble starch for storage
       • Used for respiration
       • Converted into fats and oils for storage.
       • Used to produce cellulose which strengthens cell walls
   • Measuring the Distribution of Organisms
     • The distribution of living things in their natural enviroment can be measured.
     • The data can be used to find the range, mean, median and mode of the measurements.
     • Random sampling using a transect
     • Sample size is important. In a large field, enough quadrats must be placed to be sure the sample is representive of the whole field.

6. Enzymes

   • Proteins, Catalysts and Enzymes
     • Proteins are made up of long chains of amino acids.
     • Enzymes are proteins which act as biological catalysts.
     • Enzymes are large proteins and the shape of an enzyme is vital for its function.
       • This shape has an area where other molecules can fit. This is called an active site.
     • The substrate in a reaction can be held in the active site and can be either connected to another molecule or it can be broken down.
     • What can an enzyme do?
       • Build large molecules from many smaller ones
       • Change one molecule into another one.
       • Break down large molecules into smaller ones.
   • Factors affecting enzyme action
     • Factors which alter the shape of the active site prevent the enzyme from working.
     • Enzyme activity is affected by temperature and pH.
     • Reactions take place faster when it is warmer. At higher temperature, the molecules move around quicker and collide with each other more often and with more energy.
     • If the temperature gets too hot the enzyme stops working because the active site changes shape. We say that the enzyme becomes denatured,
   • Enzymes in Digestion
     • Digestive enzymes are made by glands in the digestive system.
     • Digestive enzymes work outside the body cells in the cavity of the digestive system.
     • Specific enzymes digest each particular food type.
   • Speeding up Digestion
     • Enzymes work best in a narrow pH range.
     • Protease enzymes in the stomach work best in acid conditions. Glands in the stomach wall produce hydochloric acid to create very acidic conditions.
     • Amylase and Lipase work in the small intestine. They work best when the conditions are slightly alkaline.
     • Bile is produced in the liver and stored in the gall bladder.
       • Bile only neutralises acid, it does not contain enzymes.

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