Biology Paper 1

• Chromosomes


  Coiled up lengths of DNA molecules
• Chromosomes


  • Each chromosome carries a large number of genes
  • Different genes control the development of different characteristics, e.g. hair colour
• Body cells normally have two copies of each chromosome, one from the mother and one from the father
• Villi


  Tiny little projections covering the inside of the small intestine
• Villi


  • Increase surface area so that digested food is absorbed much more quickly into the blood
  • Have a single layer of surface cells
  • Have a very good blood supply to assist quick absorption
• Function of the muscle cell


  1. Contract quickly

  2. Are long to have space to contract

  3. Contain lots of mitochondria to generate energy needed for contraction
• Phloem and xylem cells

  • Form phloem and xylem tubes
  • Transport substances such as food and water around plants
• Formation of phloem and xylem tubes

  Cells are long and joined end to end
• Xylem cells


  • Hollow in the centre
• Phloem cells


  • Have very few subcellular structures, so stuff can flow through them
• Growth and DNA replication

  1. In a cell that's not dividing, the DNA is all spread out in long strings

  2. Before it divides, the cell has to grow and increase the amount of subcellular structures such as mitochondria and ribosomes

  3. It then duplicates its DNA - so there's one copy for each new cell

  4. The DNA is copied and forms X shaped chromosomes

  5. Each 'arm' of the chromosome is an exact duplicate of the other
• Cell components (plant and animal cells)

  • Nucleus
  • Cell membrane
  • Cytoplasm
  • Mitochondria
• Organ system


  A group of organs working together to perform a particular function
• Digestive system


  1. Breaks down and absorbs food

  2. Glands produce digestive juices

  3. Stomach and small intestine digest food

  4. Liver produces bile

  5. Small intestine absorbs soluble food molecules

  6. Large intestine absorbs water from undigested food, leaving faeces
• Function of sperm cells


  To get the male DNA to the female DNA
• Sperm cells


  • Have a long tail and streamlined head to help it swim to the egg
  • Have many mitochondria to provide the energy needed
  • Carry enzymes in the head to digest through the egg cell membrane
• Root hair cells


  Cells on the surface of plant roots that grow out into the soil as long "hairs" to increase the surface area for absorbing water and minerals
• Phloem and xylem cells


  • Form tubes that transport substances such as food and water around plants
  • Are long and joined end to end to form the tubes
  • Xylem cells are hollow in the centre and phloem cells have very few subcellular structures to allow flow of substances
• Function of nerve cells

  • To carry electrical signals from one part of the body to another
  • Are long to cover more distance and have branched connections at their ends to connect to other nerve cells and form a network
• Mitosis


  1. Chromosomes line up at the centre of the cell

  2. Cell divides the two arms of each chromosome to opposite ends

  3. Membranes form around each set of chromosomes to become the nuclei of the two new cells

  4. Cytoplasm and cell membrane divide to produce two new identical daughter cells
• Electron microscope


  • Uses electrons instead of light to form an image
  • Has much higher magnification and resolution than light microscopes
  • Allows viewing of very small internal structures like mitochondria, chloroplasts, ribosomes and plasmids
• Stem cells


  • Found in plant meristems (growth regions)
  • Can differentiate into any type of plant cell
  • Can be used to quickly and cheaply produce clones of whole plants, including rare species
  • Can be used to grow crops of identical plants with desired features like disease resistance
• Using a light microscope

  1. Clip slide onto stage

  2. Select lowest-powered objective lens

  3. Use coarse adjustment to move stage up close to objective

  4. Look through eyepiece and use coarse adjustment to roughly focus

  5. Use fine adjustment to get clear image

  6. Swap to higher-powered objective to see slide with greater magnification
• Salivary glands


  Produce amylase enzyme in the saliva
• Stomach


  • Pummels the food with its muscular walls
  • Produces the protease enzyme
  • Produces hydrochloric acid to kill bacteria and give the right pH for the protease enzyme to work
• Liver


  Where bile is produced
• Bile


  Neutralises stomach acid and emulsifies fats
• Gall bladder


  Where bile is stored, before it's released into the small intestine
• Large intestine


  Where excess water is absorbed from the food
• Nerve cells


  • Carry electrical signals from one part of the body to another
  • Are long to cover more distance
  • Have branched connections at their ends to connect to other nerve cells and form a network throughout the body
• Muscle cells


  • Contract quickly
  • Are long so they have space to contract
  • Contain lots of mitochondria to generate the energy needed for contraction
• Increase in temperature


  Increases the activation energy of the atoms or molecules and therefore increases their net movement across a partially permeable membrane, increasing the rate of diffusion
• Preparing a slide to view onion cells

  1. Add a drop of water to the middle of a clean slide

  2. Cut up an onion and separate it into layers, use tweezers to peel off some epidermal tissue from the bottom of one of the layers

  3. Place the tissue into the water on the slide

  4. Add a drop of iodine (a stain)

  5. Place a cover slip on top (try not to get any air bubbles under there)
• Stem cells


  May be able to cure many diseases
• Medicine uses adult stem cells to

  • Cure disease, e.g. stem cells transferred from the bone marrow of a healthy person can replace faulty blood cells in the patient
• Embryonic stem cells


  Could be used to replace faulty cells in sick people, e.g. make insulin-producing cells for people with diabetes, nerve cells for people paralysed by spinal injuries
• Cell cycle


  Body cells in multicellular organisms divide to produce new cells as part of a series of stages
• Mitosis


  The stage of the cell cycle when the cell divides
• Mitosis in multicellular organisms

  • Used to grow or replace cells
  • Results in two new identical cells to the original cell, with the same number of chromosomes
• Differentiation


  The process by which a cell changes to become specialised for its job