Biology p1

• Eukaryotic cells

  Animal and plant cells are eukaryotic cells. They have genetic material (DNA) that forms chromosomes and is contained within a nucleus.
• Animal cell

  • Cell membrane: controls the movement of substances into and out of a cell
  • Nucleus: contains DNA
  • Mitochondria: where energy is released through respiration
  • Ribosomes: site of protein synthesis
  • Cytoplasm: jelly-like substance where chemical reactions happen
• Plant cell

  • Cell membrane
  • Permanent vacuole: contains cell sap
  • Nucleus
  • Chloroplast: contains chlorophyll to absorb light energy for photosynthesis
  • Cell wall: made of cellulose, which strengthens the cell
• Prokaryotic cells

  Bacteria have the following characteristics: single-celled, no nucleus - have a single loop of DNA, have small rings of DNA called plasmids, smaller than eukaryotic cells
• Prokaryotic cell

  • Cell wall
  • Cell membrane
  • Flagellum
  • Bacterial DNA loop (no nucleus)
  • Cytoplasm
  • Plasmid DNA ring
• 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.
• To calculate the magnification of an image

  Magnification = Image size / Actual size
• Specialised cells

  Cells in animals and plants differentiate to form different types of cells. Most animal cells differentiate at an early stage of development, whereas a plant's cells differentiate throughout its lifetime.
• Specialised cells

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

  • Has a 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

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

  • Has branched endings, called dendrites, to make connections with other neurones or effectors
  • Has a myelin sheath that insulates the axon to increase the transmission speed of the electrical impulses
• Root hair

  • Has a long projection to speed up the absorption of water and mineral ions by increasing the surface area of the cell
  • Has lots of mitochondria to release energy for the active transport of mineral ions from the soil
• Palisade cell

  • Has lots of chloroplasts containing chlorophyll to absorb light energy
  • Is located at the top surface of the leaf where it can absorb the most light energy
• Cytoplasm

  The jelly-like substance inside a cell, in which the organelles are suspended
• DNA

  The genetic material that carries the instructions for the development and functioning of living organisms
• Diffusion is the spreading out of particles, resulting in a net movement from an area of higher concentration to an area of lower concentration.
• Osmosis is the diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane.
• Active transport is the movement of particles from a more dilute solution to a more concentrated solution using energy from respiration. Particles move against the concentration gradient - from an area of low concentration to an area of high concentration.
• The steeper the concentration gradient

  The faster the rate of diffusion
• The higher the temperature

  The faster the rate of diffusion
• Single-celled organisms have a large surface area-to-volume ratio, allowing enough molecules to be transported across their cell membranes to meet their needs.
• Multicellular organisms have a small surface area-to-volume ratio, meaning they need specialised organ systems and cells to allow enough molecules to be transported into and out of their cells.
• Exchange surfaces

  • Have a large surface area
  • Have a thin membrane
  • Have a good blood supply
• Exchange surfaces

  • Villi in the small intestine
  • Alveoli in the lungs
  • Fish gills
  • Root hair cells
• Chromosomes are made of DNA molecules and carry a large number of genes.
• In normal body cells, the chromosomes are normally found in pairs.
• The cell cycle

  1. Cell grows bigger

  2. DNA replicates (chromosomes are duplicated)

  3. Increase in number of sub-cellular structures such as ribosomes and mitochondria

  4. Complete set of chromosomes is pulled to each end of the cell

  5. The nucleus divides to form two nuclei

  6. Cytoplasm and cell membrane divide to form two identical daughter cells
• Cell division by mitosis is important for the growth and repair of cells, and for asexual reproduction.
• Stem cell

  An undifferentiated cell that can develop into one or more types of specialised cell
• Types of stem cell in mammals

  • Adult stem cells
  • Embryonic stem cells
• Adult stem cells

  • Found in specific parts of the body in adults and children, can only differentiate into certain types of cells
• Embryonic stem cells

  • Found in early human embryos, can differentiate into any type of specialised cell in the body
• Where are stem cells found?

  • Adult stem cells: Bone marrow
  • Embryonic stem cells: Early human embryos
  • Plant stem cells: Meristem regions in the roots and shoots
• What can stem cells differentiate into?

  • Adult stem cells: Certain types of cells
  • Embryonic stem cells: Any type of specialised cell
  • Plant stem cells: All plant cell types
• Advantages of adult stem cells

  • Fewer ethical issues, established technique for treating diseases, relatively safe to use
• Advantages of embryonic stem cells

  • Can treat a wide range of diseases, may be possible to grow whole replacement organs, no donor needed