Biology

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Microscopy

Magnification is the degree to which the size of an image is larger than the object itself = how much bigger?

Resolution is the degree to which you can distinguish between two separate points that are very close together. The higher the resolutoin, the more detail you can see = how clear?

Light microscope - 1500x

                                   - 200nm resolution

Electron microscope - 500 000x (TEM)

                                    - 100 000x (SEM)

                                   - 0.1 nm resolution

 

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Organelles

Nucleus contains chromatin (stores DNA), controls the activity of the cell through encoded proteins and brings about cell division. Dense region in the centre called a nucleolus which makes RNA and ribosomes, which are bothe used for protein synthesis.

SER synthesises and transports lipids

RER is studded with ribosomes which synthesise proteins that can be processed and transported by the RER

Golgi apparatus receives proteins and modifies them (by adding a sugar molecule) it then packages them into golgi vesicles which transport them to the plasma membrane

Mitochondrion has an inner and outer membrane. The inner membrane is folded into cristae and the central space is called the matrix, it is also studded with enzymes which are the site for ATP synthesis.

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Organelles 2

Chloroplast have 3 membranes - an inner, outer and thylakoid (folded into discs and stacked into grana). The stacks of grana are in the stroma and are connected to each other by lamellae. Chlorophyll molecules (on membranes) are the site of photosynthesis and ATP synthesis.

Ribosomes are the site of protein synthesis, also translates mRNA into the correct sequence of amino acids to produce a specific protein.

The cytoskeleton is a network of fibres made of protein that keep the cells shape staple. Some fibres, called actin filaments, are able to cause movement. Microtubules can also cause movement of the organelles, such as moving chromosomes and golgi vesicles.

Undulipodia and cilia produce movement by bending from side to side. Microtubules slide against each other using dynein arms, the axoneme bends and the base stays anchored.

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Cell Membranes

  • separate cell contents
  • cell recognition and signalling
  • hold components of metabolic pathways in place
  • regulate transport of materials in and out of cells

Permeable to small, polar and non-polar molecules. Impermeable to large, polar molecules, ions, sugars and amino acids. Permeability increases with temperature.

Glycoproteins are involved in cell signalling by acting as a receptor site (antigen), help bind cells together in tissues, provide binding sites for drugs and keep the membrane stable by forming H-bonds with H2O.

Channel proteins provide a channel for larger, polar molecules to pass through the membrane via facilitated diffusion down a concentration gradient.

Carrier proteins can also transport large molecules by facilitated diffusion as well as large or polar substances via active transport which requires energy. They are specific to a certain molecule and have a complemantary shape to it.

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Cell Division

Interphase: G1 - proteins made (and organelles replicated)

                   S - synthesis of new DNA (chromosomes replicated)

                   G2 - growth

Prophase - chcromosomes become visible, nuclear envelope starts to break down

Metaphase - nuclear membrane disappears and chromosomes line up along equator

Anaphase - chromosomes pulled apart at the centromere to opposite poles

Telophase - new nuclear membranes form and cytokinesis takes place, in animal cells a cleavage furrow forms and pinches together to separate the 2 daughter cells, in plant cells a cell plate forms where the spindle equator was and eventually becomes a new cell membrane and wall.

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Spirometer

A spirometer is a chamber filled with oxygen that floats on a tank of water, when someone breathes in the chamber moves down. Carbon dioxide that is breathed out into the apparatus need to be absorbed by soda lime.

Initially the volume or air in the spirometer drops slowly. This is because oxygen is used up in respiration and carbon dioxide is then expelled which is absorbed by the soda lime, reducing the overall volume of air in the spirometer.

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Transport Systems

Reasons for a transport system are:

  • size
  • SA:V ratio
  • level of activity

As an animal gets bigger its layers of cells increase and nutrients find it harder to reach cells deeper within the body. The SA:V ratio gets smaller and the SA is not large enough to supply all the oxygen and nutrients needed by the internal cells. The demand for these in a very active organism is often high, meaning the SA also finds it hard to keep up with the demand.

In summary: Diffusion distance is increased and diffusion takes longer meaning, substances cannot get to internal cells in time so transport systems are needed to help the organism be more efficient.

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Blood vessels

Arteries carry blood away from the heart. They have no valves as the blood can move under its own high presure without any risk of backflowing, however it has a small lumen to try and maintain this high pressure. It also has collagen to help it withstand the high presures. It has a thick tunica media with lots of elastic fibres and smooth muscle (used in vasodilation and vasoconstriction).

The veins don't carry blood under a high pressure so have to have valces throuhout to prevent a backflow of blood. It also has a large lumen to make the passage of blood at this low pressure easier. It too contains elastic fibres, smooth muscle and collagen, although not as much as the arteries, to help with the stretch and recoil as the heart pumps.

Capillaries have a basement membrane and squamous epithelial cells to reduce the diffusion distance ie./ for oxygen diffusion at alveoli. It's also very narrow so as to force RBC's up against its wall to furthe reduce diffusion distance. It carries slow flowing blood under a low pressure and has no valves, but does have pores in the membrane to allow molecules in and out easliy.

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Fetal haemoglobin

Points from mark scheme:

  • fetal haemoglobin has a higher affinity for oxygen than maternal haemoglobin
  • fetal haemoglobin takes up oxygen in a lower partial pressure of oxygen
  • placenta has a low partial pressure of oxygen
  • at low partial pressure the adults haemoglobin will dissociate its oxygen

 

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Water moving up xylem

Points from mark scheme:

  • water moves into xylem down a water potential gradient
  • by root pressure - high hydrostatic pressure at bottom of xylem
  • evaporation at leaf - low hydrostatic pressure at top of xylem
  • water moves up from high hydrostatic to low hydrostatic
  • water pulled up under tension in a continuous stream
  • cohesion between water molecules
  • adhesion of water molecules to xylem
  • capillary action - xylem narrow so water rises

 

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