OCR Biology F211

CELLS
1. MICROSCOPES
  1. MAGNIFICATION: the degree to which an image is larger than the object itself.
  2. RESOLUTION: the ability to clearly distinguish between two objects that are very close together.
  3. LIGHT MICROSCOPE
    1. Uses a number of lenses to produce an image.
      1. Light passes from the bulb under the stage, through a condenser lens then through the specimen.
        This light is focussed through the objective lens then through the eyepiece lens
        To view things at different magnifications different objective lenses can be rotated into position.
        Usually four lenses are present. X4, X10, X40 and the X10 lens is an oil immersion lens.
        The eye piece them magnifies the image usually by X10.
    2. Max magnification of X1500
    3. Max resolution 200nm.
    4. Wide range of specimen
  4. SEM
    1. Resolution of 0.1 nm.
    2. Magnification of X100,000
    3. SEM gives a 3D image so cell surface structures can be seen.
  5. TEM
    1. Resolution of 0.1nm
    2. Magnification of X500,000
    3. 2D picture but allows details of organelles to be seen.
  6. Staining
    1. White blood cells cant be seen without it
    2. Creates a higher contrast within the cell
    3. Acetic Orcein stains DNA red.
    4. Electron micrographs are coloured using software.
  7. I A M
2. ORGANELLES
  1. Nucleus: largest organelle, houses genetic information
  2. Nucleolus, dense sphere inside nucleus. makes ribosomes and RNA
  3. Nuclear envelope: surrounds nucleus Double membrane with nuclear pores allowing mRNA through
  4. R/S ER: Continuous with nuclear envelope, ER has ribosomes.
    1. RER transports proteins made by ribosomes,
    2. SER Involved in the making of lipids
  5. Golgi apparatus: stack of flattened membrane bound sacs. Used to modify proteins and package them into vesicles.
  6. Mitochondria: sausage shaped, double membrane. Where ATP is made.
  7. Lysosomes:Spherical sacs, single membrane Contain digestive enzymes to break down organelles pathogens and cells.
  8. Chloroplasts: only in plants. Two membranes, contains thylakoids. Site of photosynthesis.
  9. Plasma membrane: phospholipid bilayer. controls what enters and exits the cell.
  10. Centrioles: small tubes of protein fibres, pair next to nucleus. Form spindle fibres during cell divistion
  11. Flagella and cilia, hair like extensions from the surface of a cell. Move using ATP.
    1. Cytoskeleton
      1. provides strength support and stability.
      2. Determines the shape of the cell
      3. moves organelles e.g mitochondria.
      4. moves vesicles
      5. micro tubules do not move they provide an anchor for protein to move along.
      6. Cilia move out of time with eachother to produce a wave.
  12. Ribosomes: tiny, some in cytoplasm some attached to RER, site of protein synthesis.
    1. PROTEIN SYNTHESIS
      1. 1) The gene is copied onto mRNA
        2) mRNA leaves the nucleus through a nuclear pore.
        3) mRNA attaches to a ribosome.
        4) ribosome reads the instructions on the gene to assemble a protein.
        5) Molecules are 'pinched off' in vesicles and travel towards the golgi apparatus.
        6)Vesicle fuses with the golgi apparatus
        7) golgi apparatus processes and packages the molecules, ready for release.
        8) The molecules are pinched off in vesicles from the golgi apparatus and moves towards the cell surface membrane
        9) vesicles fuse with cell surface membrane.
        10) cell surface membrane opens to release molecule to the outside, this is exocytosis.
3. DIFFERENCES
  1. Prokaryotes
    1. No nucleus.
    2. One membrane
    3. no membrane bound organelles
    4. cell wall made of peptidoglycan
    5. smaller ribosomes
    6. Circular DNA
  2. Plant
    1. Cell wall
      1. made of cellulose
        Sieve like network of strands.
      2. kept rigid by pressure inside cell
        comes from vacuole.
        maintains stability.
CELL MEMBRANES
1. USES
  1. Outside cells
    1. Seperate cell contents from outside environment
    2. Cell recognition and signalling
    3. regulating transport of materials.
  2. Inside cells
    1. form organelles
    2. Provides selective permeability
2. STRUCTURE
  1. Plasma membranes are partially permeable.
  2. A bilayer of phospholipid molecules forms the main structure, intrinsic and extrinsic proteins are studded within the bilayer.
  3. Phospholipids have a fatty acid tail and hydrophillic head. They are permeable to small non-polar molecules.
  4. Cholesterol provides stability and makes the structure more complete.
  5. Glycolipids are hospholipds with a carbohydrate attached, used for cell signalling, cell surface antigens and cell adhesion.
  6. Proteins allow for charged and large molecules to travel through the cell membrane
  7. Glycoproteins.
    1. act as antigens
    2. Enable self-recognition.
    3. Used in cell signalling
    4. act as receptor sites for hormones
    5. allow cell adhesion
3. EFFECTS OF TEMPERATURE
  1. Increasing temperature gives the molecules more energy, which makes the membrane leaky. Meaning random molecules can move in and out of the cell.
  2. The membrane structure is disrupted and the phospholipid bilayer melts and membrane proteins are denatured. The membrane becomes more permeable.
4. CELL SIGNALLING AND RECEPTORS
  1. Cell signalling
    1. A process that leads to communication and coordinated between cells, such as hormones binding to their receptor sites.
  2. Hormones are used in cell signalling. The target cells have a receptor which is complementary to the hormone meaning it can bind to the receptor cells triggering the desired internal response.
  3. Beta blockers are used to prevent a muscle from increasing the heart rate to a dangerous level and some schizophrenia drugs mimic a natural neurotransmitter which some individuals cannot produce.
5. TRANSPORT
  1. Passive transport
    1. Diffusion is the movment of molecules from an area with a high concentration to an area with a low concentration, small non-polar substances
    2. Facilitated diffusion requires ATP. channel proteins move ions, carrier proteins carry lage molecules through.
  2. Active transport is the movement of molecules or ions against a concentration gradient.
    1. Mineral ions moved into root hair cells.
    2. Hydrogen ions moved out of companion cells.
    3. Miovement of sucrose out os sieve tube at sink.
  3. Endocytosis, active transport of large quantities of a matierial into a cell using ATP.
  4. Exocytosis is the movement of large wuantities of material out of a cell from a vesicle using ATP.
  5. Osmosis is the movement of water molecules from a region of higher water potential to a region of lower water potential across a partially permeabe membrane.
    1. Pure water
      1. animal cell will burst, be haemolysed.
      2. Plant cell will become turgid.
    2. Negative water potential,
      1. Animal cell becomes crenated
      2. Plant cell is plasmolysed
DIVISION DIVERSITY AND ORGANISATION
1. THE CELL CYCLE
  1. Mitosis occupies only a small percentage of the cell cycle, the rest includes copying and checking genetic information, growth of organelles, increasing number of organelles, synthesis of proteins and ATP productioon.
  2. Stages of mitosis.
    1. Interphase: DNA replicates.
      1. Prophase: Chromosomes supercoil and become visible. nuclear envelope breaks down. Centriole divides in two and move to form spindle.
        Metaphase: chromosomes line up along the middle of the cell. They attach to a spindle thread by centromere.
        Anaphase: Sister chromatids are separate. The spindle fibres shorten pulling them apart.
        Telophase: sister chromatids reach the poles of the cell and a new nuclear envelope forms around each set. The spindle breaks down. The chromosomes uncoil and are no longer visible under a light microscope.
        Cytokinesis: the whole cell splits into two new cells. Each one genetically identical to one another. These are clones. In plant cells cytokinesis starts at the centre.
  3. Mitosis only occurs in the meristem cells in plants and there are no centrioles involved.
2. A homologous pair of chromosomes are chromosomes that have the same genes at the same loci. Members of homologous pairs pair up during meiosis. Diploid organisms produced by sexual reproduction have homologous pairs of chromosomes. One member from the mother and one from the fater.
3. Mitosis
  1. Growth: multicellular organisms produce extra cells to grow. each new cell is geneticall identical to the parent cells so cam perform the same fumction.
  2. Repair/replacement: Damaged cells need to be replaced by new ones that perform the same functions and so need the genetically identical daughter cells.
  3. Asexual reproduction: single celled organisms divide to produce two daughter cells that are seperate organisms. some multicellular organisms use asexual reproduction to produce offspring from parts of the parent.
  4. Maintains chromosome number in cells.
4. Budding: the nucleus divides by mitosis, the cell swells on one side and bulges, the nuceus, cytoplasm and organelles move into the bud and it pinches off as the cell wall forms so the bud becomes a seperate cell.
5. Meiosis produces cells that aren't genetically identical
  1. They are haploid, they produce 4 cells not 2, they are also gametes.
6. Stem cells.
  1. A cell that is unspecialised and not differentiated but is capable of mitosis and is able to differentiate and become other cell types.
    1. Differentiation is the changes occuring in cells in multicellular organisms so that each type of cell becomes specialised to form a specific function.
      1. Erythrocytes lose their nuclus, golgi apparatus and rough endoplasmic reticulum. they are filled with haemoglobin and their shape changes to a bi-concave disc giving it a large surface area to volume ratio,
      2. Neutrophils have many lisosomes, many microfilaments, many ribosomes many mitochondria and lots of golgi and many receptor sites on the surface membrane. They are flexible meaning they can engulf foreign particles more easily.
      3. Xylem and phloem
        In xylem meristem cells elongate and the walls are waterproofed by deposits of lignin which kills the cell contents. the ends of the cell breaks down forming hollow tubes with large lumen.
        In phloem the cells elongate and lose their nucleus and most of their cytoplasm, their ends to not break down completely but form sieve like plates between cells. next to each phloem cell is a companion cell which keeps it alive.
      4. Sperm cells contain many mitochondria , specialised lysosomes to break down egg wall, nucleus contains diploid number of cells. they are very small long and thin to allow movement.
      5. Palisade cells are long and thin to maximise the absorption of light and contain many chloroplasts. They have thin walla allowing easy absorption of carbon dioxide.
      6. Root hair cells increase the surface area available to absorb water and minerals from the soil.
      7. Guard cells contain spiral thickenings of cellulose making the outer wall thinner than the inner wall. In light water moves into them making them turgid opening the stoma. They containa vacuole to take up water and become turgid. They contain mitochondria to generate ATP for use in active transport.
  2. Found in meristem cells in plants which are in th e cambium, in buds, just behind the tip of the root, just behind the tip of the shoot.
7. Tissues organs and organ systems.
  1. A tissue is a group of cells working together to perform a particular function
  2. An organ is a group of tissues working together to perform a particular function
  3. An organ system is a group of organs working together to perform a particular role or function.
  4. Animal tissues.
    1. Epithelium: layers and linings
      1. Squamous epithelium. Flattened cells tha form a thin smooth surface. Used in blood vessels and alveoli held in place by basement membrane made of collagen and glycoproteins.
      2. Ciliated epithelium is column shaped exposed surface covered with cilia which move in waves. aft mucus in lungs.
    2. Connective tissues, hold structures together and provide support
    3. Muscle tissue: specialised to relax and contract
      1. the muscular and skeletal systems must work together for movement to take place, thiscan only hapen if the nervous system 'instructs' the muscles to coordinate their actions. This requires energy.
    4. Nervous tissue convert stimuli to electrical impulses and conduct them.
8. Plant specialisations
  1. Xylem are composed of xylem vessel cells and parenchyma cells.
  2. Ploem comprises of sieve tubes and companion cells. companion cells are metabolically active.
EXCHANGE SURFACES AND BREATHING
1. Exchange surfaces
  1. Multicellular organisms need specialised exchange surfaces because they have a higher demand for oxygen and other nutrients they have a smaller surface area to volume ration aswell as this their sirface area is too small for diffusion alone to to provide all the nutrients they rquire. Diffusion takes too kolg.
  2. Single celled organisms have a large surface area to volume ratio and have a low demand for oxygen or CO2 removal diffusion alone is enough to meet their needs.
  3. Alveoli produce a large surface area to volume ratio The squamous epithelium provides a short diffusion pathway. They have capillaries running over their surfaces delivering CO2 and remoxing oxygen
2. Efficient gaseous exchange
  1. Alveoli have a squamous epithelium and the surrounding arteries have a thin endothelium providing a short diffusion pathway.
    1. epithelial cells of the alveoli produce a surfactant which reduces the surface tension and prevents the alveoli collapsing when the pressure changes.
  2. erythrocytes trransport oxygen and carbon dioxide to and from the alveoli
  3. The diaphragm and intercostal muscles work together to maintain a concentration gradient.
  4. the ciliated epithelial cells and goblet cells work together to remove dust/pollen/bacteria.
  5. cartilage holds the airway open.
  6. Smooth muscle can constrict to close the airways, lastic fibres recoil adding ventilation and returning the size of the umen to normal.
  7. Macrophages and neutrophills engulf and destroy pathogens.
  8. Ventillation increases the concentration of oxygen in the alveoli so the concentration of is higher than in the blood. IT decreases the concentration of carbon dioxide so it is smaller thanin the blood, maintaining a a good diffusion gradient.
3. mammalian exchange system.
  1. Trachea and bronchi
    1. Thick walls made of several layers of tissue
    2. Regular c rings of cartilage to keep the lumen open and to allow the oesophogous to expand during swallowing.
    3. Layers of glandular tissue, connective tissue, smooth muscle elastic fibres smooth muscle and blood vessels.
    4. Inner layer has a ciliated epithelium with goblet cells.
  2. Bronchioles
    1. Much narrower than bronchi
    2. Some have cartilage some dont
    3. The wall is made mostly of smooth muscle and elastic fibres.
  3. Alveoli
    1. Wall is one cell thick
    2. 100-300um diameter
    3. Good blood supply
4. Functions
  1. Cartilage holds the trachea open. Prevents collapse
  2. Cilia move in a synchronised pattern to waft mucus that the goblet cells have secreted in order to catch bacteria and dust.
  3. smooth muscle contracts to prevent harmful substances from entering the lungs.
  4. Elastic fibres recoil returning the lumen to its original size, also they prevent alveoli from bursting.
5. Breathing
  1. Inspiration.
    1. 1) diaphragm contracts pushing digestive organs down.
      1. 2) intercostal muscles contract raising ribs.
        3) volume of thorax increases.
        4) pressure in thorax drops below atmospheric pressure
        5) air moves into lungs
  2. Expiration
    1. 1) diaphragm relaxes and is pushed up by displaced organs.
      1. 2) Intercostal muscle relax and ribs fall
        3) volume of thorax decreases
        4)pressure in thorax rises above atmospheric
        5) air is pushed out of the lungs.
  3. Spirometer
    1. A chamber filled with oxygen or fresh air floating on a tank of water. A healthy person breathes into a disinfected mouthpiece attached to a tube connected to the oxygen tank. breathing in causes the chamber to sink, breathing out causes it to rise, Lime water is used to absorb carbon dioxide. The movements of the chamber are recorded using a data logger
    2. Vitalcapacity
      1. The maximum amount of air that can be breathed in and out of the lungs in any one breath.
      2. Breathe in as much as possible then out as much as possible
    3. Tidal volume
      1. The volume of air moved in and out of the lungs during breathing at rest.
      2. breathe in and out normally whilst sitting dwn at rest
    4. Breathing rate is calculated by dividing the number of breaths by the time in minutes
    5. Oxygen uptake is measured by dividing the amount of oxygen dm3 by the time taken in seconds or minutes.
Transport in animals
1. Need for transport systems.
  1. Several layers of cells means that nutrients and oxygen will be used up by the outer layers of the organism
  2. If an animal is very active it will need a good supply of nutrients and oxygen for the energy.
  3. To allows animals to grow to a large size

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