iGCSE Biology - Life Processes

Life Processes

 

• Multicellular organisms contain many different types of cells with different structures.
• Eight life processes:

          Move – muscles in animals, slow growth movement in plants

          Respire – get energy from their food

          Stimuli – respond to changes in their surroundings

          Control – their internal conditions

          Grow – increase in size and mass

              Reproduce – produce offspring

          Excrete – get rid of toxic waste products

          Nutrition – make own food (plants) or eat other organisms                     (animals)

• Animal cell components:

          Cytoplasm – living material of cell, makes up body

          Nucleus – contains chromosomes and controls activity of cell

          Cell membrane – boundary between cytoplasm and outside,                         selectively permeable

          Mitochondria – carry out respiration

• Plant cell components:

          All of the above

          Cell wall – made of cellulose, keeps the cell’s shape, freely                     permeable

          Vacuole – contains cell sap, a store of dissolved nutrients

              Chloroplast – absorb light energy for photosynthesis, contain                     chlorophyll which makes them green

• Chemical reactions in cells are controlled by enzymes, which in turn are controlled by the genes in the nucleus
• Enzymes are biological catalysts
• Body temperature is low, so without enzymes reactions would be too slow
• The molecule that an enzyme acts upon is its substrate
• The substrate attaches itself to the active site of the enzyme
• Three factors affect rate of reactions of enzymes:

          Temperature – each enzyme has an optimum temperature,                             after which it begins to denature

          pH – enzyme activity decreases increasingly further away from                       optimal pH

          Concentration – rate of reaction increases with the                     concentration of enzyme and substrate

• Breaking down food molecules to release stored chemical energy is respiration
• glucose + oxygen → carbon dioxide + water (+energy)
• C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O
• Anaerobic respiration: Glucose à Ethanol + Carbon Dioxide
• In humans, lactic acid is produced
• Diffusion:  the net movement of particles down a concentration gradient
• Active transport: the movement of particles against the concentration gradient, using energy from respiration
• Osmosis: the net movement of water from a dilute solution to a more concentrated solution across a partially permeable membrane
• Larger surface-area to volume ratio means faster diffusion and osmosis
• Multicellular organisms begin life as a single fertilised cell, a zygote
• A zygote undergoes mitosis to grow
• As the embryo grows, cells become specialised to carry out particular   roles: differentiation
• Cells with a similar function are grouped together as tissues
• A collection of tissues carrying out a particular function is called an organ
• A collection of organs working together are called an organ system

          Digestive system – gut and glands such as pancreas and gall                           bladder

          Respiratory system – lungs, exchanges oxygen and carbon                     dioxide

          Circulatory system – heart + blood vessels, transport materials

          Excretory system – kidneys, filter waste materials from blood

          Nervous system – brain, spinal cord + nerves, coordinate body

          Endocrine system – glands secreting hormones, chemical                        messengers

          Reproductive system – produces sperm in males and eggs in                            females