biology

Cards (30)

  • Plant and animal cells (eukaryotic cells) have a cell membrane, cytoplasm and genetic material enclosed in a nucleus.
    Bacterial cells (prokaryotic cells) are much smaller in comparison. They have cytoplasm and a cell membrane surrounded by a cell wall. The genetic material is not enclosed in a nucleus. It is a single DNA loop and there may be one or more small rings of DNA called plasmids
  • Most animal cells have the following parts:
    • a nucleus
    cytoplasm
    • a cell membrane
    mitochondria
    ribosomes.
    In addition to the parts found in animal cells, plant cells often have: • chloroplasts
    • a permanent vacuole filled with cell sap.
    Plant and algal cells also have a cell wall made of cellulose, which strengthens the cell.
  • Cells may be specialised to carry out a particular function:
    sperm cells, nerve cells and muscle cells in animals
    root hair cells, xylem and phloem cells in plants.
  • As an organism develops, cells differentiate to form different types of cells.
    Most types of animal cell differentiate at an early stage.
    Many types of plant cells retain the ability to differentiate throughout life.
    In mature animals, cell division is mainly restricted to repair and replacement. As a cell differentiates it acquires different sub-cellular structures to enable it to carry out a certain function. It has become a specialised cell.
  • An electron microscope has much higher magnification and resolving power than a light microscope. This means that it can be used to study cells in much finer detail. This has enabled biologists to see and understand many more sub-cellular structures.
    Students should be able to carry out calculations involving magnification, real size and image size using the formula:
    magnification = size of image /size of real object
  • Bacteria multiply by simple cell division (binary fission) as often as once every 20 minutes if they have enough nutrients and a suitable temperature.
    Bacteria can be grown in a nutrient broth solution or as colonies on an agar gel plate.
    Uncontaminated cultures of microorganisms are required for investigating the action of disinfectants and antibiotics.
  • They should be able to explain why:
    Petri dishes and culture media must be sterilised before use
    inoculating loops used to transfer microorganisms to the media must be sterilised by passing them through a flame
    • the lid of the Petri dish should be secured with adhesive tape and stored upside down
    • in school laboratories, cultures should generally be incubated at 25°C.
  • The nucleus of a cell contains chromosomes made of DNA molecules. Each chromosome carries a large number of genes.
    In body cells the chromosomes are normally found in pairs.
  • Cell cycle
    Series of stages that cells divide through
  • Cell cycle
    1. Genetic material doubles
    2. Genetic material divided into two identical cells
  • Before cell division
    • Cell needs to grow
    • Increase number of sub-cellular structures (e.g. ribosomes, mitochondria)
    • DNA replicates to form two copies of each chromosome
  • Mitosis
    1. One set of chromosomes pulled to each end of the cell
    2. Nucleus divides
    3. Cytoplasm and cell membranes divide to form two identical cells
  • Students need to understand the three overall stages of the cell cycle but do not need to know the different phases of the mitosis stage
  • Cell division by mitosis
    Important in the growth and development of multicellular organisms
  • Students should be able to recognise and describe situations in given contexts where mitosis is occurring
  • A stem cell is an undifferentiated cell of an organism which is capable of giving rise to many more cells of the same type, and from which certain other cells can arise from differentiation.Stem cells from human embryos can be cloned and made to differentiate into most different types of human cells.
    Stem cells from adult bone marrow can form many types of cells including blood cells.
    Meristem tissue in plants can differentiate into any type of plant cell, throughout the life of the plant.Treatment with stem cells may be able to help conditions such as diabetes and paralysis.
  • Therapeutic cloning
    An embryo is produced with the same genes as the patient. Stem cells from the embryo are not rejected by the patient's body so they may be used for medical treatment.
  • The use of stem cells has potential risks such as transfer of viral infection, and some people have ethical or religious objections.
  • Stem cells from meristems in plants
    Can be used to produce clones of plants quickly and economically.
  • Rare species
    • Can be cloned to protect from extinction.
  • Crop plants with special features such as disease resistance
    • Can be cloned to produce large numbers of identical plants for farmers.
  • Diffusion
    The spreading out of the particles of any substance in solution, or particles of a gas, resulting in a net movement from an area of higher concentration to an area of lower concentration
  • Substances transported in and out of cells by diffusion
    • Oxygen
    • Carbon dioxide in gas exchange
    • Urea from cells into the blood plasma for excretion in the kidney
  • Substances may move into and out of cells across the cell membranes via diffusion
  • Factors which affect the rate of diffusion
    • Difference in concentrations (concentration gradient)
    • Temperature
    • Surface area of the membrane
  • Students should be able to explain how different factors affect the rate of diffusion
  • A single-celled organism has a relatively large surface area to volume ratio. This allows sufficient transport of molecules into and out of the cell to meet the needs of the organism.
  • In multicellular organisms, surfaces and organ systems are specialised for exchanging materials. This is to allow sufficient molecules to
    be transported into and out of cells for the organism’s needs. The effectiveness of an exchange surface is increased by:
    • having a large surface area
    • a membrane that is thin, to provide a short diffusion path
    • (in animals) having an efficient blood supply
    • (in animals, for gaseous exchange) being ventilated.
  • Water may move across cell membranes via osmosis. Osmosis is the 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 (against a concentration gradient). This requires energy from respiration.
    Active transport allows mineral ions to be absorbed into plant root hairs from very dilute solutions in the soil. Plants require ions for healthy growth.
    It also allows sugar molecules to be absorbed from lower concentrations in the gut into the blood which has a higher sugar concentration. Sugar molecules are used for cell respiration.