GCSE's

• Describe the structure of a typical animal cell:

  •nucleus: contains the genetic material, and controls the activities of the cell

  •cytoplasm: gel-like substance where most chemical reactions happen

  •cell membrane: holds the cell together and controls what goes in and out

  •mitochondria: site of aerobic respiration

  •ribosome: site of protein synthesis (where there made)
• Describe how a plant cell differs from an animal cell

  •permanent vacuole: contains cell sap (a weak solution of sugar and salts)/ maintaining its turgidity

  •chloroplast: contains chlorophyll and site of photosynthesis (absorbs light for photosynthesis)

  •cell wall: made of cellulose supports the cell strengthens it
• Respiration transfers energy that cells need to work
• Differences between prokaryotic cells and eukaryotic cells

  • Prokaryotic cells (e.g. bacterial cells):
  • Genetic material is not enclosed in a nucleus
  • Genetic material is a single DNA loop and may have one or more small rings of DNA (plasmids)
• Units of measurement


  • Centimetre (1 x 10^2 metres) cm
  • Millimetre (1 x 10^3 metres) mm
  • Micrometre (1 x 10^6 metres) μm
  • Nanometre (1 x 10^9 metres) nm
• The difference in order of magnitude between a human hair (length = 100 μm) and the HIV virus (length = 100 nm) is 47 - 4 - 7 = 36
• Plant cell wall - Provides strength, prevents the cell bursting when water enters by osmosis, supports the cell and maintains its turgidity

  Permanent vacuole - Maintains the cell's turgidity
• Permanent vacuole

  Maintains the cell's turgidity
• Sperm cells


  • Haploid nucleus containing genetic information
  • Streamlined head and long tail to aid and enable swimming
  • Mitochondria to provide energy needed for tail movement
  • Acrosome (carries enzymes) to digest egg cell membrane
• Nerve cells


  • Long axon to allow electrical impulses to be transmitted all over the body from the central nervous system
  • Dendrites from the cell body connect to and receive impulses from other nerve cells, muscles and glands
  • Myelin sheath insulates the axon and speeds up the transmission of impulses along the nerve cell
• Muscle cells


  • Arrangement of protein filaments allows them to slide over each other to produce muscle contraction
  • Mitochondria to provide energy for muscle contraction
  • Merged cells in skeletal muscle allow muscle fibre contraction in unison
• Root hair cells


  • Large surface area to absorb nutrients and water from surrounding soil
  • Thin walls that do not restrict water absorption
• What is cell differentiation?

  The process by which cells become specialised
• Why is cell differentiation important?

  Cell differentiation is important because it allows the production of different tissues and organs that perform various vital functions in the human body
• At what point in their life cycle do most animal cells differentiate?

  Most animal cells differentiate early in their life cycle
• Plant cells retain the ability to differentiate throughout their entire life cycle
• What is the purpose of cell division in mature animals?

  Repair and replacement of cells
• What changes does a cell go through as it differentiates?

  Cells become specialised through acquisition of different sub-cellular structures to enable a specific function to be performed
• Magnification - The number of times bigger an image appears compared to the size of the real object

  Resolution - The smallest distance between two objects that can be distinguished -
• Light microscope


  • Passes a beam of light through a specimen which travels through the eyepiece lens, allowing the specimen to be observed
  • Inexpensive
  • Easy to use
  • Portable
  • Can observe both dead and living specimens
  • Limited resolution
• Electron microscope


  • It uses a beam of electrons which are focused using magnets. The electrons hit a fluorescent screen which emits visible light, producing an image.
  • Greater magnification and resolution
  • Expensive
  • Large so less portable
  • Require training to use
  • Only dead specimens can be observed
• Types of electron microscope

  • Transmission electron microscope (TEM)
  • Scanning electron microscope (SEM)
• Why do electron microscopes have a greater magnification and resolution?

  Electron microscopes have a greater magnification and resolution because they use a beam of electrons which has a shorter wavelength than photons of light
• How have electron microscopes enabled scientists to develop their understanding of cells?

  - Allow small sub-cellular structures (e.g. mitochondria, ribosomes) to be observed in detail.

  - Enable scientists to develop more accurate explanations about how cell structure relates to function.
• Calculating magnification


  magnification = size of image / size of real object
• What is the formula used to calculate cross-sectional area of a bacterial colony or clear area around a bacterial colony?

  πr2

  How is the number of bacteria in a population after a certain time calculated from the mean division time?

  1. Calculate the number of times the bacteria will divide in the given time period from the mean division time. 2. Use the following equation to calculate the number of bacteria: Number of bacteria in population at end of time period = number of bacteria at the beginning of the time period x 2number of divisions in the time period .
• Calculate the number of bacteria that will be present after 3 hours for a population that divides every 15 minutes and has 5 bacterium present now

  15 minutes = 0.25 hours

  3/0.25 hours = 12 divisions

  5 x 212 =20480 or 2.048 x 104

  (try to always express the answer in standard form if possible.)
• Calculating the number of bacteria in a population after a certain time

  1. Calculate the number of times the bacteria will divide in the given time period from the mean division time

  2. Use the equation: Number of bacteria in population at end of time period = number of bacteria at the beginning of the time period x 2^(number of divisions in the time period)
• Chromosomes - Consist of DNA molecules combined with proteins, and contain genes which provide the instructions for protein synthesis

  What is a gene? - A section of DNA which codes for a protein.
• How many chromosomes are found in the nucleus of human body cells? - 46

  How many chromosomes are found in the nucleus of gametes? - 23

  How are chromosomes arranged in the nucleus of a body cell - Arranged in pairs - 46 chromosomes form 23 pairs.
• The nucleus of human gametes contains 23 chromosomes
• Chromosomes in the nucleus of a body cell are arranged in pairs
• Stages of the cell cycle

  • Replication of DNA and synthesis of organelles
  • Mitosis
  • Division of cell
• Why is mitosis important?

  • Produces identical cells which all have the same genetic information,

  • Produces additional cells for growth and repair
• Stages of the cell cycle

  First stage: DNA replicates to form two copies of each chromosome, the cell also grows and copies its internal structures such as mitochondria and ribosomes

  Second stage: Mitosis takes place, one set of chromosomes is pulled to each end of the cell, the nucleus also divides

  Final stage: Cytoplasm and cell membrane divide to form two copies of identical daughter cells
• Stem cell


  An unspecialised cell which is capable of differentiating into other cell types and of self-renewal
• Function of embryonic stem cells

  Embryonic stem cells can replicate themselves and differentiate into many other types of cells, and may be able to treat conditions such as paralysis and diabetes by dividing to replace damaged cells
• Function of adult stem cells in bone marrow

  Adult stem cells can differentiate into several cell types to replace dead or damaged tissues, e.g. bone marrow stem cells can form many different types of blood cell
• Function of stem cells in plant meristems

  Meristem stem cells retain the ability to differentiate into any type of plant cell throughout their lifespan - they can differentiate into any cell which is required by the plant
• Therapeutic cloning

  A cloning method where an embryo is produced with the same genetic makeup as the patient, so the stem cells originating from the embryo will not be rejected by the patient's immune system and can be used to treat certain medical conditions