B1

• Eukaryotic cells


  Animal and plant cells have genetic material (DNA) that forms chromosomes and is contained in a nucleus
• Cell membrane


  • Controls the movement of substances in and out of a cell
• Animal cell


  • Nucleus contains DNA
  • Mitochondria where energy is released through respiration
• Plant cell


  • Cell wall made of cellulose, which strengthens the cell
  • Permanent vacuole contains cell sap
  • Chloroplasts contain chlorophyll to absorb light energy for photosynthesis
  • Ribosomes are the site of protein synthesis
• Bacteria


  • Single-celled
  • No nucleus, have a single loop of DNA
  • Have small rings of DNA called plasmids
  • Smaller than eukaryotic cells
• Specialised cells


  • Sperm cell
  • Red blood cell
  • Muscle cell
  • Nerve cell
  • Root hair cell
  • Palisade cell
• Sperm cell


  Fertilise an ovum (egg)
• Sperm celladaptations


  • Tail to swim to the ovum and fertilise it
  • Lots of mitochondria to release energy from respiration, enabling the sperm to swim to the ovum
• Red blood cell


  Transport oxygen around the body
• Red blood cell


  • No nucleus so more room to carry oxygen
  • Contains a red pigment called haemoglobin that binds to oxygen molecules
  • Flat bi-concave disc shape to increase surface area-to-volume ratio
• Muscle cell


  Contract and relax to allow movement
• Muscle cell


  • Contains protein fibres, which can contract to make the cells shorter
  • Contains lots of mitochondria to release energy from respiration, allowing the muscles to contract
• Nerve cell


  Carry electrical impulses around the body
• Nerve cell


  • Branched endings, called dendrites, to make connections with other neurones or effectors
  • Myelin sheath insulates the axon to increase the transmission speed of the electrical impulses
• Root hair cell


  Absorb mineral ions and water from the soil
• Root hair cell


  • Long projection speeds up the absorption of water and mineral ions by increasing the surface area of the cell
  • Lots of mitochondria to release energy for the active transport of mineral ions from the soil
• Palisade cell


  Enable photosynthesis in the leaf
• Palisade cell


  • Lots of chloroplasts containing chlorophyll to absorb light energy
  • Located at the top surface of the leaf where it can absorb the most light energy
• Light microscope


  Uses light to form images, living samples can be viewed, relatively cheap, low magnification, low resolution
• Electron microscope


  Uses a beam of electrons to form images, samples cannot be living, expensive, high magnification, high resolution
• Electron microscopes allow you to see sub-cellular structures, such as ribosomes, that are too small to be seen with a light microscope
• Magnification


  Calculated as: image size / actual size
• Diffusion


  The spreading out of particles, resulting in a net movement from an area of higher concentration to an area of lower concentration. Factors which affect the rate of diffusion: difference in concentration, temperature, and surface area of the membrane.
• Osmosis


  The diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane.
• Active transport


  The movement of particles from a more dilute solution to a more concentrated solution using energy from respiration.
• Diffusion in humans


  • Nutrients in the small intestine diffuse into the capillaries through the villi
  • Oxygen diffuses from the air in the alveoli into the blood in the capillaries. Carbon dioxide diffuses from the blood in the capillaries into the air in the alveoli
  • Urea diffuses from cells into the blood for excretion in the kidney
• Diffusion in fish


  • Oxygen from water passing over the gills diffuses into the blood in the gill filaments
  • Carbon dioxide diffuses from the blood in the gill filaments into the water
• Diffusion in plants


  • Carbon dioxide used for photosynthesis diffuses into leaves through the stomata
  • Oxygen produced during photosynthesis diffuses out of the leaves through the stomata
• Osmosis in Plants


  Water moves by osmosis from a dilute solution in the soil to a concentrated solution in the root hair cell
• Active transport in Humans

  Active transport allows sugar molecules to be absorbed from the small intestine when the sugar concentration is higher in the blood than in the small intestine
• Active transport in Plants

  Active transport is used to absorb mineral ions into the root hair cells from more dilute solutions in the soil
• Xylem


  The transport tissue in plants that carry water and mineral ions from the roots to the highest leaves and shoots
• Xylem


  • Important in supporting the plant
• Xylem cells


  Cells that make up the xylem tissue
• Xylem cell formation


  1. Cells are alive when first formed

  2. Lignin builds up in spirals in the cell walls

  3. Cells die and form long hollow tubes
• Xylem cells


  • Allow water and mineral ions to move easily through them, from one end of the plant to another
  • Spirals and rings of lignin make them very strong and help them withstand the pressure of water moving up the plant
  • Help support the plant stem
• Phloem


  The specialised transport tissue that carries the food made by photosynthesis around the body of the plant
• Phloem cells


  Cells that make up the phloem tissue
• Phloem cell adaptation


  1. Cell walls between the cells break down to form special sieve plates

  2. Phloem cells lose a lot of their internal structures but are supported by companion cells that help to keep them alive

  3. Mitochondria of the companion cells transfer the energy needed to move dissolved food up and down the plant in phloem
• Phloem cells do not become lignified and die