Biology 2

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  • Biology 2
    • Gas exchange in organisms
      • SA:Vol
        • As an organism gets bigger their SA:Vol gets smaller.
        • Unicelled organisms
          • Have a very large SA:Vol, so they can exchange gases directly through the cell membrane.
      • Unicelled organisms
        • Have a very large SA:Vol, so they can exchange gases directly through the cell membrane.
      • Sponges - Hollow body
        • Being hollow increases the SA:Vol so gas can be exchanged through the cell membranes.
        • SA:Vol
          • As an organism gets bigger their SA:Vol gets smaller.
      • Tapeworms - Flattened body
        • They increase their SA:Vol by having a flat body, decreasing the diffusion distance.
      • Insects
        • They have little openings in their exoskeleton called spiracles.
          • They lead to a network of tubes called trachea.
            • These then branch into tracheoles that carry air directly to the cells.
            • The trachea and tracheoles are held open by rings of chitin.
              • These then branch into tracheoles that carry air directly to the cells.
        • To increase respiration rate, insects move their bodies up and down to maintain a concentration gradient.
          • Rate of diffusion increases.
      • Fish
        • Fish exchange gas through gills, which are composed of thousands of filaments. Each filaments is covered in lamallae containing blood capillaries.
          • This structure gives a large SA and a short diffusion pathway for gas exchange.
        • Water flows over the filaments and lamellae and oxygen diffuses down a concentration gradient. Carbon dioxide diffuses the opposite way.
        • They improve the efficiency of gas exchange by using a countercurrent flow system.
          • This is where the blood is flowing in the opposite direction to the flow of water.
            • So a concentration gradient is maintained and it never reaches equilibrium.
    • Human Circulatory System
      • Arteries
        • Composed mainly of elastic tissue.
          • So that the artery can expand and recoil depending on the pressure of the blood.
      • Arterioles
        • The muscles can contract or relax. Happens during homeostasis.
        • Contraction = Vasoconstriction
        • Relax = vasodilation
      • Capillaries
        • Where substances enter/leave the blood.
        • They have a large SA to help with diffusion.
      • Veins
        • Have large lumens to reduce resistance to blood flow. They also contain valves to stop blood flowing backwards.
      • Subsystems
        • KIDNEY
          • To kidney: Renal Artery
            • From aorta, high oxygen concentration.
          • From kidney: Renal Vein
            • To vena cava, low oxygen concentration.
        • LIVER
          • To liver: Hepatic Artery
            • From aorta, high oxygen concentration.
          • To liver: Hepatic Portal Vein
            • From small intestine, blood rich in digested food.
          • From liver: Hepatic Vein
            • To vena cava, low oxygen concentration.
        • LUNGS
          • To lungs: Pulmonary Artery
            • Low oxygen concentration, from heart
          • From lungs: Pulmonary Vein
            • High oxygen concentration, to heart
    • Tissue Fluid
      • Blood is made from; Red blood cells, white blood cells, platelets, plasma.
      • Tissue fluid is the liquid that bathes the surrounding cells. It lacks the large proteins in the plasma because they cannot pass through the capillary membrane.
        • Oxygen passes into the cells from the tissue fluid. Carbon dioxide and waste products pass into the tissue fluid from the cells.
      • Some tissue fluid does not drain back into the blood.
        • This becomes lymph
          • The lymph vessels then empty back into the subclavian veins.
      • How tissue fluid is made: Liquid leaves the capillaries at the venus end due to high hydrostatic pressure.
        • It then re-enters the blood at the other end by osmosis due to the lowered water potential in the blood.
          • The lower water potential in the blood is due to the large proteins.
    • Haemoglobin
      • In the lungs
        • Haemoglobin associates with oxygen.
        • High partial pressure of oxygen.
        • Haemoglobin has a high affinity for oxygen here.
        • Haemoglobin becomes saturated with oxygen.
      • Respiring tissues
        • Haemoglobin dissociates with oxygen.
        • Low partial pressure of oxygen here.
        • Haemoglobin has a low affinity for oxygen here.
      • Oxygen-dissociation curves
        • Shift to the right
          • Low affinity for oxygen.
          • Right=releases
        • Shift to the left
          • High affinity for oxygen.
          • Left=loves
        • Exercise: Shift to the right called the 'Bohr Shift'
          • Muscles contracting more, so greater amounts of carbon dioxide produced.
            • Acidity causes increase in the amount of oxygen to be released for the respiring tissues.
        • Small endotherms: Shift to the right.
          • They need to respire rapidly because they have a large SA:Vol and so lose heat quickly.
        • Low oxygen levels: Shift to the left
          • Haemoglobin can become fully saturated with oxygen even when the surroundings are at a low partial pressure.
        • Foetal haemoglobin: Shift to the left.
          • Foetal blood will become saturated when the adult haemoglobin is releasing oxygen.
        • Myoglobin: Shift to the left.
          • This is a pigment in the muscles which stores oxygen. It becomes saturated with oxygen when oxygen is released by haemoglobin.
    • Transport in Plants
      • How water crosses the root.
        • The root hair cell will have a lower water potential than the soil, so water moves in by osmosis. The water potential in the xylem is the lowest so the water will move towards the xylem.
        • The APPOPLAST pathway: via the cell wall.
          • The casparian strip causes the water to go through the cell membrane which allows for screening.
        • The SYMPLAST pathway: via the cytoplasm.
      • Th way water moves up the xylem.
        • Cohesion-tension theory.
          • Water moves into the xylem by osmosis. It is then drawn up the xylem since transpiration from the leaf causes tension.
            • The molecules of water form a continuous stream due to the cohesion between the water molecules. The water diffuses out of the stomata in the leaves.
        • Root pressure
          • Cells around the xylem secrete minerals which decreases the water potential. More water moves into the xylem by osmosis. This creates a push from beneath.
      • Potometer
        • This is used to measure the rate of water uptake or the rate of transpiration by a plant.
    • The Cell Cycle.
      • Interphase consists of 3 phaese; The first growth phase, Synthesis (DNA replication), Second growth phase.
      • Before a cell has divided the DNA is checked to make sure the replication is correct.
      • DNA mutations disrupt the cell cycle. This can be caused by: Radiation, smoking, chemicals, pollutants, viruses.
    • Polysaccharides
      • These are long chains of many monomers joined together by glycosidic bonds.
      • Starch.
        • Plant storage polysaccharide made of ALPHA glucose.
        • It is insoluble and so does not change the water potential of the plant cell.
        • It is a mixture of amylose and amylopectin.
          • Amylose: 1-4 bonds, helix with hydrogen bonds.
          • Amylopectin: 1-4 and 1-6 bonds, more ends so broken down quicker.
      • Glycogen
        • Animal storage polysaccharide, made of ALPHA glucose.
        • Mainly in the muscle and liver cells.
        • It has 1-4 bonds with some 1-6. so it can be broken down rapidly.
      • Cellulose.
        • structure in plant cells, made of BETA glucose.
        • They had 1-4 bonds but alternate glucose molecules are inverted.
        • They form straight chains which are linked together by hydrogen bonds to form microfibrils.
          • Microfibrils are strong and rigid.
    • Meiosis
      • Produces gametes which contain a haploid nucleus.
        • Responsible for variation.
      • DNA unravels and replicates so there are two copies of each chromosome called chromatids.
        • The DNA condenses to form double-armed chromosomes.
          • Meiosis I - the chromosomes arrange themselves in homologous pairs.
            • The homologous pairs are then separated, halving the chromosome number.
              • Meiosis II - the pairs of sister chromatids are separated.
                • Four Haploid cells that are genetically different.
            • Chromatids wrap around each other. Crossing over ocurs.
    • Mitosis
      • Interphase - DNA replication/growth.
      • Prophase - DNA condenses, chromosomes visicle as sister chromatids joined at the centromere, spindle apparatus forms, nuclear membrane disintegrates.
      • Metaphase - Centromeres line up on equator, spindle fibres attach to chromosomes and pull apart by centromeres.
      • Anaphase - Spindle fibres shorten, pulling chromosomes to the poles.
      • Telophase - When reach different poles nuclei membrane reforms, spindle apparatus disappears.
      • Followed by cytokinesis.
    • Courtship
      • To select a healthy mate.
      • To avoid aggression especially in solitary animals.
      • To ensure mating occurs with a member of the same species.
      • To synchronise breeding behaviour.
    • Classification
      • Kingdom--> Phylum--> Class--> Order--> Family--> Genus--> Species.
      • Species: A group of similar organisms that can reproduce to give fertile offspring.
      • The name given to an organism is the genus then species.
      • There are no overlap between taxonomic groups.
      • DNA hybridisaton.
        • DNA from two different species are collected and the hydrogen bonds are broken so they are only single stranded.
          • Where the base sequences are the complementary the single strands will form hydrogen bonds.
            • The DNA is then heated to separate the strands. The higher the temp. the more hydrogen bonds formed so the more alike the species are.
    • Antibiotics and Resistance
      • They are drugs that inhibit or kill the growth of a bacteria.
      • Inhibiting the synthesis of the protein links between the molecules in the cell wall.
        • By interfering with protein synthesis.
          • By inhibiting DNA replication.
      • Vertical gene transmission
        • Bacteria reproduce asexually, if the parent bacteria has the gene for resistance then it is passed to the daughter bacteria.
      • Horizontal gene transmission
        • Two bacteria join by a cytoplasmic bridge, a plasmid containing the resistance gene is replicated and passed to the other bacteria. Called conjugation.

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