Cell biology

• Eukaryotes


  Cells contain their genetic material (DNA) enclosed in a nucleus
• Eukaryotic cells


  • Animal cells
  • Plant cells
• Prokaryotes


  Genetic material (DNA) is not enclosed in a nucleus
• Prokaryotic cells are much smaller than eukaryotic cells
• Prokaryotic cell


  • Bacterial cell
• Order of magnitude


  Every order of magnitude is 10x greater than the one before
• Animal cells


  • Nucleus stores the DNA
  • Cytoplasm is a watery solution where chemical reactions take place
  • Cell membrane controls the molecules that can enter and leave the cell
  • Mitochondria are where aerobic respiration takes place
  • Ribosomes are the sites of protein synthesis
• Plant cells


  • Have a regular shape
  • Chloroplasts contain chlorophyll and they're the sites of photosynthesis
  • Cell wall is made from cellulose and this strengthens the cell
  • Vacuole is filled with cell sap and helps give the plant cell its shape
• Most animal cells are specialised and have adaptations which help carry out their particular function
• Differentiation


  When cells become specialised
• Sperm cells


  • Job is to join with an ovum (egg cell)
  • Contain DNA in the nucleus but only half the genetic information of a normal adult cell
  • Long tail which allows them to swim to the ovum
  • Streamlined to make swimming easier
  • Packed with mitochondria which provides energy needed for swimming
  • Contain enzymes which allow them to digest their way through the outer layer of the ovum
• Nerve cells


  • Job is to send electrical impulses around the body
  • Axon carries the electrical impulses from one part of the body to another
  • Myelin insulates the axon and speeds up the transmission of nerve impulses
  • Synapses are at the end of the axon and allow the impulse to pass from one nerve cell to another
  • Dendrites increase surface area so that the other nerve cells can connect easily
• Muscle cells


  • Can contract (get shorter)
  • Protein fibres which can change their length
  • Packed with mitochondria for energy for muscle contraction
  • Muscle cells work together to form muscle tissue
• Root hair cells


  • Increase surface area of the root, absorb water and dissolved minerals more effectively
  • Do not contain chloroplasts because they are underground
• Xylem cells


  • Form long tubes that carry water and dissolved minerals from roots to leaves
  • Have very thick walls containing lignin which provides support to the plant
  • End walls between cells have broken down so water and dissolved minerals flow easily
  • No nucleus, cytoplasm, vacuole or chloroplasts
• Phloem cells


  • Carry dissolved sugars up and down the plant
  • Have no nucleus and limited cytoplasm
  • End walls have pores called sieve plates which allow dissolved sugars to move through
  • Each phloem vessel cell has a companion cell connected by pores
  • Mitochondria provides energy
• Optical microscope


  • Stage where you place the microscope slide
  • Lenses above the stage with different magnifications
  • Eyepiece where you look through
  • Coarse and fine focusing dials
• Total magnification


  Magnification of the eyepiece lens * magnification of objective lens
• Light microscopes


  Have limited magnification and resolution
• Electron microscopes


  Have much greater magnification and resolution than light microscopes
• Magnification


  Size of image / size of real object
• Chromosomes


  Found in the nucleus, made of the molecule DNA
• Body cells contain 2 of each chromosome, they are paired
• Human body cells contain 23 pairs of chromosomes
• Gametes have chromosomes that are not paired
• Chromosomes carry a large number of genes
• Cell cycle


  1. DNA replicates to form 2 copies of each chromosome

  2. Mitosis takes place, nucleus divides

  3. Cytoplasm and cell membrane divide to form 2 identical cells
• Mitosis


  • Essential for growth and development of multicellular organisms
  • Takes place when an organism repairs itself
  • Happens during asexual reproduction
  • Extremely highly controlled
• Stem cells


  Undifferentiated cells which can give rise to more cells of the same type and can differentiate to form other types of cells
• Bone marrow transplant


  1. Patient's existing bone marrow is destroyed using radiation

  2. They receive a transplant of bone marrow from a donor

  3. Stem cells in the bone marrow now divide and form a new one, differentiating to form blood cells
• Therapeutic cloning


  • An embryo is produced with the same genes as the patient
  • Stem cells from embryo can be transplanted into patient without being rejected
  • Once inside, the stem cells differentiate to replace cells which have stopped working
• Plant stem cells


  • Roots and buds contain meristem tissue which can differentiate into any type of plant tissue at any point in life
  • Can clone a rare plant or cloned crop plants
• Diffusion


  The spreading out of particles resulting in an overall movement from area of higher concentration to lower concentration
• Oxygen concentration


  Higher outside the cell, so oxygen moves into the cell by diffusion
• Carbon dioxide concentration


  Higher inside the cell, so carbon dioxide moves out of the cell by diffusion
• Urea concentration


  Waste product produced inside cells, diffuses out of the cells into blood plasma and excreted by kidneys
• Concentration gradient


  The difference in concentrations, greater concentration means faster rate of diffusion
• Osmosis


  The diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane
• Plant cell in water

  Water moves in, cell expands and becomes turgid
• Plant cell in concentrated solution


  Water moves out, cell shrinks and becomes flaccid