cell biology

• eukaryotic cells contain their genetic material enclosed in a nucleus
• prokaryotic cells contain genetic material which is not enclosed in a nucleus

  they are also smaller than eukaryotic cells
• cytoplasm

  • watery solution where chemical reactions take place
• cell membrane

  • controls the molecules that can enter and leave the cell
• mitochondria

  • where aerobic respirations takes place
• ribosomes

  • the sites of protein synthesis
• chloroplasts (plants only)

  • contains chlorophyll
  • site of photosynthesis
• cell wall (plants only)

  • made up of cellulose
  • strengthens the cell
• vacuole (plants only)

  • filled with cell sap
  • helps with the plant's shape
• • most animal cells are specialised which means they have adaptations which help them carry out their functions. when cells become specialised, scientists call this differentiation.
• how are sperm cells adapted?

  • long tail- allows them to swim the ovum
  • packed with mitochondria - provides energy needed for swimming
  • enzymes - allows them to digest their way though the outer layer of the ovum
  • genetic information in the nucleus which is only half the genetic information of a normal adult cell
• how are nerve cells specialised?

  • long axon - carries electrical impulses
  • myelin insulates the axon - speeds up the transmissions of nerve impulses
  • synapses - allow the impulse to pass from one nerve cell to another
  • dendrites - increases the surface area so other nerve cells can connect more easily
• how are muscle cells specialised?

  • packed full of mitochondria - provide energy for muscle contraction
  • work together to form muscle tissue
  • protein fibres
• how are root hair cells specialised?

  • hairs - increase surface area of the root so it can absorb more water and dissolved minerals
  • no chloroplasts - underground (cannot carry out photosynthesis)
• how are xylem vessels specialised?

  • very thick wall containing lignin - provides support for the plant
  • end wall between cells have broken down - cells now form long tube so water and dissolved minerals flow easily
  • no internal structures - easier for water and minerals to flow
• how are phloem cells specialised?

  • no nucleus and only limited cytoplasm
  • end walls have pores called sieve plates - allows dissolved sugars to move through the cell interior
  • mitochondria - provides energy
• light microscopes vs electron microscope

  • EM microscopes have a greater magnification and resolution than LM
• mitosis

  1. the DNA replicates to form two copies of each chromosomes and the cell grows
  2. mitosis takes place when one set of chromosomes is pulled to each end of the cell (nucleus also divides)
  3. The cytoplasm and the cell membrane divides to form two identical cells
• functions of mitosis

  • essential for growth and development of multicellular organisms
  • takes place when an organism repairs itself
  • happens during asexual reproduction
• stem cells

  an undifferentiated cell which can give rise to more cells of the same type and can differentiate to form other types of cells
• bone marrow transplants (leukaemia)

  • patient's existing bone marrow is destroyed using radiation
  • patient receives a transplant of bone marrow from a donor
  • stem cells in the bone marrow now divide to form a new bone marrow. they also differentiate and form blood cells.
• problems w stem cells

  • donor has to be compatible with the patient, if not, white blood cells produced by the donated bone marrow could attack the patient's body
  • risk of viruses
• therapeutic cloning

  • an embryo is produced with the same genes as the patient
  • stem cells from the embryo can be transplanted into the patient without being rejected by the patient's immune system
  • once inside the patient, stem cells then differentiate to replace cells which have stopped working correctly
• meristem tissues

  stem cell which can differentiate into any type of plant tissue

  use meristem to clone a rare plant from going extinct
• diffusion

  spreading out of particles resulting in a net movement from an area of high concentration to an area of lower concentration
• factors which affect the rate of diffusion

  • difference in concentration - greater the concentration gradient, the faster diffusion
  • temperature - higher the temperature, greater the diffusion
  • surface area of the cell - the larger the SA, the greater the diffusion
• osmosis

  diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane
• active transport

  moves substances from a more dilute solution to a more concentrated solution
• AT vs Diffusion

  • diffusion - particles move down the concentration gradient and doesn't require energy from respiration
  • AT - particles are moved against the concentration gradient and does require energy from respiration