AI Explain

• Double circulation

  When the blood goes through the heart 2 times to complete a full cycle around the body
• Allele

  Different form of a gene
• Chromosome

  Length of DNA and contains gene
• Hormone

  Chemical secreted by the endocrine glands, carried by the blood and alters the activity of target organs
• Homeostasis

  Maintain a constant internal environment
• Population

  A group of organisms of the same species living in the same habitat at the same time
• Excretion

  Removal from the body of toxin substances, waste product of metabolism and substance excess requirement
• Active transport

  Movement of ions or large molecules through the cell membrane using carrier proteins and energy from respiration
• Species

  Group of organisms that can reproduce fertile offspring
• Gene

  Length of DNA that codes for a protein
• All life consists of cells
• Light microscope

  • Can see cells and nucleus, but not subcellular structures
• Electron microscope

  • Can see finer details and subcellular structures, has better resolving power and higher resolution
• Calculating cell size

  1. Measure image size

  2. Divide by magnification
• Cell types

  • Eukaryotic cells
  • Prokaryotic cells
• Eukaryotic cells

  • Have a nucleus where DNA is found
• Prokaryotic cells

  • Don't have a nucleus, DNA is in a ring called a plasmid
• Cell structures

  • Cell membrane
  • Cell wall (in plant cells and bacteria)
  • Cytoplasm
  • Mitochondria
  • Ribosomes
  • Chloroplasts (in plant cells)
  • Permanent vacuole (in plant cells)
  • Enzymes
• Cell membrane

  Keeps everything inside the cell, semi-permeable
• Cell wall

  Provides rigid structure (in plant cells and bacteria)
• Cytoplasm

  Liquid that makes up the cell, where most chemical reactions take place
• Mitochondria

  Where respiration takes place, releasing energy for the cell
• Ribosomes

  Where proteins are assembled or synthesized
• Chloroplasts

  Contain chlorophyll, where photosynthesis takes place (in plant cells)
• Permanent vacuole

  Stores sap (in plant cells)
• Enzymes

  Biological catalysts that break down larger molecules into smaller ones
• Types of enzymes

  • Carbohydrases (break down carbohydrates into sugars)
  • Proteases (break down proteins into amino acids)
  • Lipases (break down lipids/fats into glycerol and fatty acids)
• Enzyme specificity

  They work on a lock and key principle, only breaking down certain molecules
• Enzyme activity and temperature

  Rate increases with temperature until active site changes shape and enzyme denatures
• Enzyme activity and pH

  Rate is optimum at a certain pH, can denature at too high or too low pH
• Practical on enzyme activity

  1. Mix enzyme with substrate at different temperatures or pH

  2. Measure time taken for all substrate to be broken down

  3. Plot graph to find optimum temperature or pH
• Food tests can identify nutrients: iodine for starch, Benedict's solution for sugars, Biuret's reagent for proteins, ethanol for lipids
• Diffusion

  Movement of molecules/particles from high to low concentration, down a concentration gradient, passive
• Osmosis

  Diffusion of water across a semi-permeable membrane
• Factors affecting diffusion and osmosis

  Concentration difference, temperature, surface area
• Practical on osmosis

  1. Cut equal-sized vegetable cylinders

  2. Weigh and place in sugar solutions

  3. Reweigh after a day

  4. Calculate percentage change in mass

  5. Plot graph to find concentration with no change
• Active transport

  Using energy to move substances against a concentration gradient
• Cell types

  • Nerve
  • Muscle
  • Root hair
  • Xylem
  • Phloem
  • Stem
• Stem cells

  Unspecialised cells that can develop into different cell types
• Cloning plants can prevent extinction or produce crops with specific characteristics