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biology A-level > 2.1.5 membranes > Flashcards

2.1.5 membranes Flashcards

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1
Q

what is active transport

A

the movement of particles from an area of low concentration to an area of high concentration, up the concentration gradient across a partially permeable membrane. this requires energy released from respiration

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2
Q

what is diffusion

A

the movement of particles from an area of high concentration to an area of low concentration, down the concentration gradient across a partially permeable membrane.

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3
Q

what is osmosis

A

the movement of water from an area of high water potential to an area of low water potential, down the concentration gradient across a partially permeable membrane

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4
Q

what is the difference between simple and facilitated diffusion

A
  • facilitated diffusion is faster than simple
  • facilitated diffusion requires channel proteins to let through the molecules, simple does not
  • simple diffusion only lets through small and non-polar molecules, whereas facilitated diffusion lets through larger, polar molecules
  • simple diffusion is only limited by the concentration gradient, whereas facilitated is limited by number of proteins as well
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5
Q

what molecules does simple diffusion let through

A
  • vitamins A and D,
  • small polar molecules (e.g. water),
  • steroid hormones (oestrogen, testosterone),
  • oxygen and carbon dioxide molecules
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6
Q

what molecules does facilitated diffusion let through

A
  • polar molecules e.g. Na+ or Cl- ions
  • large molecules e.g. glucose (also polar)
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7
Q

what factors affect diffusion

A
  • pressure
  • temperature
  • steepness of concentration gradient
  • surface area of membrane
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8
Q

differences between active transport and diffusion

A
  • active transport requires specific carrier proteins in the membrane, diffusion does not
  • active transport requires energy released from respiration, diffusion does not
  • active transport is an active process, diffusion is a passive process
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9
Q

what is bulk transport and what are the two main types

A
  • the movement of large molecules or molecules of large quantities in or out of a cell. this requires energy released from respiration
  • endocytosis
  • exocytosis
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10
Q

what is endocytosis

A

the process by which the cell surface membrane engulfs material, forming a vesicle around it. this requires energy released from respiration

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11
Q

what happens in endocytosis

A
  • the unwanted particles are invaginated by the membrane (surrounded)
  • a vesicle is formed (the membrane breaks off to create an enclosed sac)
  • the membrane reattaches to itself to reform a sealed cell
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12
Q

what is endocytosis used for

A
  • urea, lactic acid (to prevent toxic build up)
  • phagocytosis (immune response to pathogens)
  • pinocytosis (taking in extracellular fluids)
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13
Q

what is exocytosis

A

the process by which materials are removed from or transported out of cells by isolating them in a vesicle. this requires energy released from respiration

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14
Q

what happens in exocytosis

A
  • a secretory vesicle is formed around the particles inside the cell by the golgi body
  • the vesicle is carried to the membrane and fuses to it
  • the unwanted particles are then slid over the membrane through the layers, forcing them out of the cell
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15
Q

what is exocytosis used for

A
  • enzymes (e.g. protease to prevent proteins which the cell is made of being broken down)
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16
Q

what is water potential

A

the measure of the quantity of water compared to solute, measured as the pressure created by water molecules. it can be determined by the number of ‘free’ water molecules in comparison to water molecules which are bound to the solute
- water potential is represented by the symbol ‘Ψ’

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17
Q

how is water potential measured

A
  • in kPa (KiloPascals)
  • pure water has a water potential 0kPa, the highest possible value
  • all water with a water potential lower than pure water has a negative value of kPa
18
Q

what is the name of the membrane around a cell and its contents

A

the protoplast

19
Q

what is the name of the membrane around a vacuole in plant cells

A

the tonoplast

20
Q

what is a hypertonic solution

A

a solution where water potential is higher inside the cell than outside

21
Q

what is an isotonic solution

A

a solution where water potential is equal in and out of the cell

22
Q

what is a hypotonic solution

A

a solution where water potential is lower inside the cell than outside

23
Q

what happens to plant cells in hypertonic solutions

A

plasmolysis- water leaves the cell by osmosis, causing the protoplast to begin to peel back from the cell wall, the cell wall maintains cell structure however the protoplast will become flaccid
- at an extreme level, a plant cell can become completely plasmolysed, where the protoplast detaches from the wall entirely

24
Q

what happens to animal cells in hypertonic solutions

A

water leaves the cell, causing it to shrivel and become crenated

25
Q

what happens to cells in isotonic solutions

A

water enters and leaves the cell at the same rate

26
Q

what happens to plant cells in hypotonic solutions

A

water enters the cell via osmosis, causing the protoplast to become turgid, however the cell wall will maintain structure

27
Q

what happens to animal cells in hypotonic solutions

A

water enters the cell via osmosis, causing the cell to swell and become haemolysed, this can cause the cell to burst

28
Q

what is a phospholipid

A
  • a form of lipid with a phosphate and glycerol head and a tail made of saturated and unsaturated fatty acids
  • the head of a phospholipid is hydrophilic, and the tail is hydrophobic, making them polar
29
Q

how are the hydrophobic tails of phospholipids protected

A

they form a phospholipid bilayer, where the tails are on the inside and the heads outside

30
Q

how are phospholipid bilayers drawn

A

can be represented in a fluid mosaic model- this is because the bilayer is not in a set structure, and its components can move around when necessary

31
Q

what are glycolipids and what is their role

A

carbohydrate chains attached to lipids (i.e. phospholipids) which form specific shapes. Act as antigens in order to be recognised as non-foreign cells

32
Q

what are extrinsic proteins and what is their role

A

proteins which are located on the surfaces of the membrane. they maintain the structure and are hydrophilic, so attract water to the cell

33
Q

what are intrinsic proteins and what is their role

A

proteins which go through the entire membrane layer. they let larger and polar molecules into the cell through facilitated diffusion

34
Q

what are the three types of intrinsic protein and what are their functions

A

channel proteins- allow diffusion of polar molecules (ions, water) by forming pores in the membrane
carrier proteins- used for active transport as the contain ATP (energy source)
gated channel proteins- only allow molecules through in certain conditions (have specific binding sites for different particles and only open their ‘gate’ in certain temperatures, voltages, pHs etc.)

35
Q

what is a glycoprotein and what are their roles

A

a carbohydrate chain bonded to an extrinsic protein. they act as receptors for cell signaling, neurotransmitters, peptide hormones and cell adhesion

36
Q

what is the role of cholesterol in the cell membrane

A
  • lipids break down in warm conditions, so cholesterol helps to maintain structure in the membrane when there is an increase in temperature by holding together the phospholipids. this prevents the membrane becoming too permeable
  • in cold conditions the membrane solidifies and becomes less permeable, so cholesterol creates space in between the phospholipids to maintain membrane fluidity and permeability
  • although cholesterol attaches to the phospholipid tails, they are polar molecules so work with the heads too
37
Q

what is cell signalling and what is it needed for

A

the process by which cells communicate with one another. it is needed in multicellular organisms to coordinate and control our bodies and responses

38
Q

what are examples of cell signalling

A
  • neurotransmission along a synapse, movement of a nerve impulse
  • hormones
  • cell recognition
  • cell adhesion
  • cell growth/replication
39
Q

what is the process of cell signaling

A
  • the sending cell releases ligands (signal molecules)(this can be from the same cell as the receptor, for instance in cell growth and replication)
  • the ligands reach the target cell and bind to the receptor (made of glycolipids or glycoproteins and are complementary to the ligand)
  • transduction takes place, where a reception is transferred into a (usually chemical) signal
  • this triggers a change to something in the cell, usually in gene expression
40
Q

what are some uses of cell signalling

A
  • beta blockers (block receptors in heart muscle cells to prevent increased heartrate/palpitations, can be used to help treat anxiety)
  • botox (a bacterial toxin from clostridium botulinum, which binds to receptors in muscle cells to prevent contraction, essentially paralysing the muscle)
41
Q

what are some examples of cell signalling going wrong

A
  • pathogens e.g. viruses (enter cell by binding to receptors and also prevent cells from carrying out functions in order to destroy it or multiply in it)
  • HIV (binds to the CD4 receptor on T-cells to prevent immune response and attack immune system)
  • autoimmune diseases (immune cells don’t recognise body cell receptors and therefore attack them)
  • tumours/cancer (cell growth/replication ligands are over- released, causing disfunction and uncontrollable and rapid replication)
  • type 2 diabetes (cells no longer respond to receiving insulin hormone ligands)

biology A-level (2 decks)

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