Unit 1 AQA AS Biology Cells & Movement

Unit 1 AQA AS Biology Cells & Movement

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- Cell surface membrane is the plasma membrane around the cell. The plasma membrane surrounds the organelles. Made up of lipids and proteins, regulates inputs and outputs of cell.

- Nucleus is the largest organelle. Nuclear envelope - double membrane, controls ins and outs, contains reactions within. Nuclear pores - allow passage of large molecules. Nucleoplasm - jelly like material makes up the cell. Chromatin - chromosomes when cell is not dividing. Nucleolus - makes ribosomal RNA and assembles ribosomes. Acts as control centre through production of mRNA and hence protein synthesis, genetic material and RNA and ribosomes.

- Microvilli, tiny finger like projections of the plasma membrane, found in cells involved with absorption. Increase surface area of the plasma membrane.

- Mitochondria, oval shaped, double membrane surrounds. Inner folded to form cristae these provide large surface area for the attachment of enzymes in respiration, production of ATP from respiration.

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- Lysosome, round organelles containing digestive enzymes, isolate harmful enzymes and digest unwanted material.

- Ribosome, site where proteins are made, protein synthesis.

- Rough Endoplasmic Reticulum, sheet like membranes enclose falttened sacs (cisternae), provides large surface area for synthesis of proteins.

- Smooth Endoplasmic Reticulum, synthesis stores and transports lipids & carbohydrates.

- Golgi Apparatus, flattened sacs, vesicles are squeezed from the ends. Packages and processes lipids and proteins received from ER, forms lysosomes.


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Observed size and Natural size need to be in the same units.

mm >> µm X1000

µm >> mm /1000

mm >> nm X1000,000

Magnification is how many times bigger the image is compared to the object.

Resolution is the minimum distance apart that two objects can be in order for them to appear as separate. Greater resolution means greater clarity and detail.

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Resolving power depends on the wavelength/form of radiation used.

Light microscope - wavelength 0.2µm - objects 0.2µm apart will be seen separate, objects closer the 0.2µm will be seen as one.

Electron microscope - wavelength 0.1nm - objects 0.1nm apart seen as separate, objects closer the 0.1nm will be seen as one.

Light microscope has poorer resolution power due to its bigger wavelength.

Light Microscope - use a stain to distinguish cell from background, needs to be cut thin in order to let light pass through.

Electron Microscope - vacuum (molecules will absorb the electrons and blur image), living things cannot be observed.

Transmission Electron microscope - images of thin slices, denser parts absorb more electrons - darker, 2-D image.

Scanning Electron Microscope - electrons bounced off surface, 3-D image.

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Cell Fractionation - process where cells are broken up and the different organelles are separated out.

Needs to be -

  • Cold - reduce enzyme activity that might break down organelles
  • Isotonic - (solution with same WP) to prevent organelles bursting or shinking
  • Buffered - maintain constant pH

1st Stage - Homogenation - Cells broken down using homegeniser, releasing organelles. Homogenate is resultant fluid, filtered to remove any full cells.

2nd Stage - Ultracentrifugation - Homogenate is separated by a ultracentrifuge, spins to create centrifugal force. Heaviest organelles forced to the bottom, supernatent is transferred to another tube and spun again - higher speed. Less dense needs higher speeds, separated out last.

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Cell Surface Membrane -

Fluid Mosaic Model - fluid as the individual phospholipid molecules move relative to one another, mosaic due to the proteins varying in size, shape, pattern and position.

Bilayer of phospholipid molecules -

Hydrophilic head (glycerol & phosphate) - attracted to water inside the cytoplasm or outside the cell.

Hydrophobic tail (fatty acid) - not attracted to water, point to the center of membrane. Unsaturated fatty acids increase permeability, saturated decrease permeability.

Enables lipid soluble molecules to pass through, restricts passage of ions and polar (water soluble) molecules.

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Proteins -

Extrinsic (not completely across) - mechanical support to membrane/recognition sites. Intrinsic (one side to another) - carriers/channels to transport ions and polar molecules across membrane. Carriers aid facilitated and active transport. Channels aid facilitated.

Carbohydrates attached to lipids or proteins - glycolipids/glycoproteins, receptors, cell-cell recognition acting as antigens, so that foreign antigens can be recognised.

Diffusion (passive) - 'net movement of molecules/ions from a region of higher conc to a region of lower conc, until molecules are evenly distributed.'

Factors effecting rate -

  • conc gradient - greater difference = faster rate
  • area - larger s.area = faster rate
  • thickness of exchange - thinner = faster rate

Rate of diffusion = s.area X conc difference/length of diffusion pathway

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Facilitated Diffusion (passive, channel and carrier) - 'net movement of polar molecules from a region of higher conc to a region of lower conc via carrier molecules.'

Protein channels - open when specific molecule is present.

Protein carriers - specific molecules bind to the protein, causing it to change shape & the molecule is released onto the other side.

Active transport - 'movement of molecules/ions, from a region of lower conc to a region of higher conc (against conc gradient) using energy (ATP) and carrier proteins.'

Decreasing respiration decreases active transport -

  • lowering temp (less KE)
  • lack of oxygen
  • metabolic and respiratory inhibitors

Carrier proteins accept molecule, molecule binds to receptors on channels, ATP binds to protein on inside - ADP and phosphate, changes shape & opens, phosphate combines with the ADP to form ATP - reverts to original.

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Osmosis - net movement of water molecules from a region of higher water potential to a region of lower water potential,through a partially permeable membrane.'

Movement continues until its isotonic, there is still movement but no net.

Water potential is the ability of water molecules to move, when solute is added the ability of water molecules to move is reduced (negative).

Pure water is 0. Movement from 0 >>> negatives.

Red blood cells - put in isotonic solution so there is no net movement of water.

Sodium potassium pump - more then one molecule moved at the same time, one moving in and out. Sodium ions actively removed, potassium pumped in.

Co-transport - sodium removed via sodium potassium pump, higher conc of sodium in lumen of small intestine, sodium ions diffuse down con gradient through different protein carrier, pairing with glucose via facilitated diffusion. Glucose transported back into the blood.

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Small intestine absorption -

Lined with Villi (with microvilli) -

  • increase surface area for diffusion
  • very thin walled (reducing diffusion path)
  • able to move, helping to maintain diffusion gradient, muscles contracting and relaxing mixing the contents of small intestine, ensuring that when glucose is absorbed new glucose replaces the area.
  • well supplied with blood vessels. so that blood can carry away absorbed molecules and maintain conc gradient.
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Natalie Beard


Nice resource, one suggestion i have is that maybe you could make the font bigger on the cards with little text on? Just to make it a little easier to read, also, what about making use of the bold button? :)

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