gcse biology

• Levels of organisation in organisms


  • Organelles
  • Cells
  • Tissues
  • Organs
  • Systems
• Cell structures


  • Nucleus
  • Cytoplasm
  • Cell membrane
  • Cell wall
  • Mitochondria
  • Chloroplasts
  • Ribosomes
  • Vacuole
• Functions of cell structures


  • Nucleus
  • Cytoplasm
  • Cell membrane
  • Cell wall
  • Mitochondria
  • Chloroplasts
  • Ribosomes
  • Vacuole
• Similarities and differences in the structure of plant and animal cells
• Characteristics of living organisms


  • Require nutrition
  • Respire
  • Excrete waste
  • Respond to surroundings
  • Move
  • Control internal conditions
  • Reproduce
  • Grow and develop
• Pathogen


  May include fungi, bacteria, protoctists or viruses
• Viruses are not living organisms. They are small particles, smaller than bacteria; they are parasitic and can reproduce only inside living cells; they infect every type of living organism. They have a wide variety of shapes and sizes; they have no cellular structure but have a protein coat and contain one type of nucleic acid, either DNA or RNA.
• Common features of eukaryotic organisms


  • Plants
  • Animals
  • Fungi
  • Protoctists
• Plants


  Multicellular organisms; their cells contain chloroplasts and are able to carry out photosynthesis; their cells have cellulose cell walls; they store carbohydrates as starch or sucrose
• Animals


  Multicellular organisms; their cells do not contain chloroplasts and are not able to carry out photosynthesis; they have no cell walls; they usually have nervous co-ordination and are able to move from one place to another; they often store carbohydrate as glycogen
• Fungi


  Organisms that are not able to carry out photosynthesis; their body is usually organised into a mycelium made from thread-like structures called hyphae, which contain many nuclei; some are single-celled; their cells have walls made of chitin; they feed by extracellular secretion of digestive enzymes onto food material and absorption of the organic products; they may store carbohydrate as glycogen
• Protoctists


  Microscopic single-celled organisms. Some have features like an animal cell, while others have chloroplasts and are more like plants. A pathogenic example is Plasmodium, responsible for causing malaria.
• Prokaryotic organisms (bacteria)


  Microscopic single-celled organisms; they have a cell wall, cell membrane, cytoplasm and plasmids; they lack a nucleus but contain a circular chromosome of DNA; some can carry out photosynthesis but most feed off other living or dead organisms
• Bacteria


  • Lactobacillus bulgaricus
  • Pneumococcus
• Diffusion


  Simple, unicellular organisms can rely on diffusion for movement of substances in and out of the cell
• Multicellular organisms need a transport system
• Structure of the thorax


  • Ribs
  • Intercostal muscles
  • Diaphragm
  • Trachea
  • Bronchi
  • Bronchioles
  • Alveoli
  • Pleural membranes
• Alveoli adaptation for gas exchange


  Diffusion between air in the lungs and blood in capillaries
• Diffusion


  Process by which substances move into and out of cells
• Factors affecting rate of diffusion


  • Surface area to volume ratio
  • Distance
  • Temperature
  • Concentration gradient
• Biological consequences of smoking in relation to the lungs and circulatory system, including coronary heart disease
• Balanced diet should include appropriate proportions of carbohydrate, protein, lipid, vitamins, minerals, water and dietary fibre
• Structure of carbohydrates, proteins and lipids


  Starch and glycogen from simple sugars, protein from amino acids, and lipid from fatty acids and glycerol
• Food tests for glucose, starch, protein and fat
• Components of the diet and their functions


  • Carbohydrate
  • Protein
  • Lipid (fats and oils)
  • Vitamins A, C and D
  • Mineral ions calcium and iron
  • Water
  • Dietary fibre
• Energy requirements


  Vary with activity levels, age and pregnancy
• Structure and function of the human alimentary canal


  • Mouth
  • Oesophagus
  • Stomach
  • Small intestine (duodenum and ileum)
  • Large intestine (colon and rectum)
  • Pancreas
• Adaptation of small intestine for absorption

  Structure of a villus
• Osmosis and active transport


  Processes by which substances move into and out of cells
• Food moved through the gut by peristalsis
• Role of digestive enzymes


  Digestion of starch to glucose by amylase and maltase, digestion of proteins to amino acids by proteases, digestion of lipids to fatty acids and glycerol by lipases
• Effect of temperature changes on enzyme function


  Changes to the shape of active site
• Bile is produced by the liver and stored in the gall bladder
• Role of bile


  Neutralising stomach acid and emulsifying lipids
• Effect of pH changes on enzyme function

  Altering the active site
• Mineral ions required by plants

  Magnesium ions for chlorophyll, nitrate ions for amino acids
• Photosynthesis


  Process of converting light energy to chemical energy
• Photosynthesis equation


  Word equation and balanced chemical symbol equation
• Factors affecting rate of photosynthesis

  Carbon dioxide concentration, light intensity, temperature
• Origin of carbon dioxide and oxygen as waste products of metabolism and their loss from the stomata of a leaf