Biology Chapter 4: Cell membranes and Transport
State how the structure of a phospholipid differs from a triglyceride. [2]
1) 2 fatty acid tails in phospholipid and 3 fatty acids for triglyceride. 2) Phosphate group is present in phospholipid but glycerol in triglyceride.
State what is meant by the term 'glycoprotein'. [1]
1) A protein combined with a carbohydrate.
Describe the role of centrioles in mitosis. [2]
1) Assembles the microtubules to form spindle fibres in prophase. 2) There is centrioles at both poles, helping the spindle fibres to contract at anaphase.
Explain how endocytosis occurs at a cell surface membrane. [3]
1) Attachment of substances to receptor 2) Infolding of membrane 3) Fusion of membrane 4) Formation of vesicle
Describe the role of the cell surface membrane during phagocytosis. [3]
1) Bacteria's antigen is recognised by the receptor 2) Antibody on bacteria combines with receptor 3) Opsonisation occurs 4) Membrane infolds and engulfs 5) membrane fuses to form vesicle enclosing bacteria
Explain the importance of the cell surface membranes to cells. [3]
1) Barrier from surroundings/external environment 2) Controls entry and exit of substances 3) Enables cell recognition 4) Allow binding of receptors for hormones 5) Cell to cell adhesion 6) Location for enzyme pathways/working 7) formation of hydrogen bonds with water for stability
Explain why calcium ions do not pass through the phospholipid bilayer. [2]
1) Calcium ions are water soluble 2) Phospholipid bilayer is hydrophilic.
Bacteria cells behave in a similar way to plant cells when immersed in solutions of different water potential. Suggest and explain what would happen to bacteria placed in a solution with a water potential more negative than their cell contents. [3]
1) Cell contents shrink; cytoplasm shrinks 2) Cell membrane peels away from cell wall; plasmolysis occur 3) There is movement of water out by osmosis 4) down the water potential gradient; higher water potential to lower water potential
Suggest and explain what would happen to bacteria placed in a solution with a water potential more negative than their cell contents. [3]
1) Cell contents/cytoplasm shrinks 2) Cell membrane peels away from the cell wall 3) Water moves out by osmosis 4) down a water potential gradient
Suggest and explain the features of a membrane transport protein. [4]
1) Channel protein has quaternary structure, and there is hydrophobic core. 2) Hydrophilic R groups on amino acids face inwards, it is globular 3) This allows facilitated diffusion and increases the permeability for osmosis 4) There is no specific binding site at channel protein; it is not selective.
Suggest and explain the features of an OmpF porin as a membrane transport proteins. [4]
1) Channel proteins 2) This protein has a quaternary structure 3) Hydrophilic R groups of the protein face inwards towards channel 4) no binding sites and it is globular 5) It allows facilitated diffusion
Describe three roles of the proteins in cell surface membrane. [3]
1) Channel proteins for facilitated diffusion 2) Carrier proteins for active transport 3) Cell recognition 4) Receptor 5) Cell to cell adhesion 6) enzyme
List four features of cell suface membranes of eukaryotic cell. [4]
1) Cholesterol 2) Glycoproteins 3) Glycolipids 4) Channel proteins 5) Carrier proteins 6) extrinsic proteins 7) receptors 8) Glycocalyx 9) attachment to cytoskeleton
Explain why cells of the body need to be supplied with cholesterol. [2]
1) Components of membranes 2) Membrane stability 3) Regulating the fluidity of the membrane 4) Production of steroid hormones
One of the functions of a plant hormone known as cytokinin is to act as a cell signalling molecule and promote cytokinesis. Suggest how cytokinin acts as a cell signalling molecule. [3]
1) Cytokinin, which is a hormone acts at target cell 2) They bind to the receptor, which is specific to the cytokinin. 3) The receptor is located in cell surface membrane. 4) When binded, it triggers secondary messenger and activates enzyme. 5) These action acts intracellularly.
Explain how flatworms survive without a transport system for respiratory gases. [4]
1) Flatworms are thin and flat 2) They have high surface area to volume ratio 3) Body surface is gas exchange surface: diffusion of O2 and CO2 4) There are short diffusion distance; no cell is far from the surface
Explain what is meant by the term 'fluid mosaic'. [2]
1) Fluid- phospholipid and protein molecules move within their monolayer. 2) Mosaic- proteins are scattered around their monolayer. There are different types of proteins.
Outline the process of cell signalling. [4]
1) Hormone is released into bloodstream and reaches the target cell in blood stream 2) Hormone is chemical signal/signalling molecules 3) Hormone binds to the receptor on cell membrane. 4) Receptor's shape is complementary to hormone 5) The binding triggers/stimulates reactions within the cell leading to enzyme cascade reaction 6) Cell signalling results in a response
State why aquaporins are necessary in cell surface membranes. [1]
1) Increases permeability of membrane to water 2) Osmosis across bilayer does not supply cell rapidly enough with water 3) Phospholipids are relatively impermeable to water.
Explain how the structure of a phospholipid molecule makes it suitable for its function in cell membranes. [3]
1) It has hydrophilic phosphate head and hydrophobic tails and this forms part of bilayer 2) Fatty acid tails may be saturated or unsaturated. 3) The head of phospholipid forms hydrogen bonds with water and stabilises the membrane 4)The unsaturated fatty acids contribute to fluidity of membrane, and is barrier to hydrophilic substances
Suggest how the increase in the proportion of phospholipids with unsaturated fatty acids helps plants survive decrease in temperature. [2]
1) Kinks prevents close packing of phospholipids at lower temperature 2) This keeps/maintains fluidity of cell membrane 3) it also prevents damage to the membranes by preventing freezing
Suggest why a transporter protein is required for the removal of ammonium ions from D.discoideuin. [2]
1) NH4+ ions are positively charged; it is water soluble 2) otherwise ammonium ion cannot pass through phospholipid bilayer.
Explain why carrier proteins are required in cell surface membrane. [2]
1) Needed for facilitated diffusion and active transport. 2) Some substances are water soluble so they can't pass through hydrophobic core.
State one role of sodium ions in organisms. [1]
1) Nerve impulses 2) Maintain osmotic potential of body fluids or osmotic balance of body 3) Urine formation/osmoregulation 4) Absorption of glucose/co-transport
The amoeboid cells of D.discoideuin feed on protein-rich material and break it down to form NH4+. The cell membranes of D.discoideuin have transporter proteins that are responsible for the excretion of NH4+ ions. Describe what happens to the NH4+ ions excreted by D.discoideuin into the soil. [3]
1) Nitrification 2) Ammonium ions to nitrite ions 3) Nitrite ions to nitrate ions by Nitrobacter 4) Nitrate is absorbed by plants.
Outline how penicillin acts on bacteria and suggest why penicillin has little or no effect at treating disease caused by Gram-negative bacteria. [3]
1) Penicillin acts on growing cells and weakens the cell wall. 2) It inhibits enzyme for cross linkage formation and prevents formation of it between peptidoglycan 3) It is less effective on Gram-negative bacteria as the outer membrane prevents the entry of penicillin 4) Proteins in the outer membrane may pump out antibiotic 5) antibiotic cannot cross hydrophobic region of outer membranes.
Explain how the structure of phospholipids allow the formation of the phospholipid layer of cell membranes. [3]
1) Phosphate head is hydrophilic 2) Fatty acid is hydrophobic 3) so heads face watery environment 4) fatty acids form hydrophobic core
Describe the structure of the cell membrane. [4]
1) Phospholipid bilayer 2) Phospholipids have hydrophilic heads and hydrophobic tails 3) The phospholipid molecules are liable to move within their monolayer 4) proteins molecules are scattered; they can also move 5) There are many different proteins like carrier proteins, channel proteins 6) There are cholesterol
Explain how phospholipid causes them to form the layer in the cell membrane. [3]
1) Polar/hydrophilic head 2) is attracted to the aqueous environment 3) Non-polar/ hydrophobic tail 4) is repelled away from the aqueous environment
Channel proteins are examples of transmembrane protein. The polypeptides are held together and also interact with phospholipids in the membrane. Suggest how the polypeptides are held together and suggest how they interact with phospholipids. [3]
1) Polypeptides are held together by bonds between R groups like ionic bond and hydrogen bond 2) Polypeptides are interacted with phospholipids: hydrophilic side of R group of amino acid interacts with the hydrophilic head of phospholipid. 3) Regions with hydrophobic R groups of amino acids interact with hydrophobic tails of phospholipid.
Explain why sodium ions across cell surface membranes by facilitated diffusion or active transport and not by simple diffusion. [3]
1) Sodium ions are hydrophilic 2) so it can't pass through hydrophobic core of phospholipid bilayer 3) so it must pass through transport proteins or carrier proteins
Suggest why some substances cannot move out of cells. [2]
1) Substances are too large 2) Polar substances can't pass through hydrophobic region of membrane. 3) There are no specific protein in membrane.
Higher temperature can damage cell membranes. Describe how proteins become denatured at high temperature and explain how this could lead to damaging cell membranes. [3]
1) The protein loses its tertiary structure, so loses active site; loses globular structure 2) The ionic/hydrogen bond breaks 3) This makes the function of proteins in membranes to be lost. 4) They are unable to receive cell signal and transport polar molecules. 5) This makes the cell membrane to lose partially permeable nature.
Suggest how a substance acts as a signalling molecule. [3]
1) They act at the target cell 2) They bind to the receptor which is in cell surface membrane 3) The shape of the receptor is complementary for the substances 4) This binding sets off a response: enzyme cascade reaction 5) They can act extracellularly or intracellularly.
State why triglycerides and phospholipids cannot be described as polymers. [1]
1) They are not composed of monomers
Explain how a phospholipid is suited to its role in cell membranes. [3]
1) They can form a bilayer; they form hydrophobic core 2) Hydrophilic head forms H bonds with water 3) Having more unsaturated fatty acids make more fluid
Platelets metabolise linoleic acid to produce 'thromboxane'. Thromboxane is released by platelets when blood loss occurs. Thromboxane acts on smooth muscle cells in the walls of arteries. This causes arteries to constrict, which reduces the blood flow. Explain why the constriction of arteries following blood loss is an example of cell signalling. [4]
1) Thromboxane is a cell signalling molecule 2) and is released into blood 3) Muscle is the target cell. 4) Thromboxane binds to the receptors 5) Thromboxane is complementary to the receptor. 6) The response is smooth muscle cell contraction 7) This happens by the activation of G protein, leading to the cascade of enzyme reaction
Describe the process of active transport. [3]
1) Transport is against the concentration gradient 2) ATP is required 3) Carrier protein is used in this process 4) There is conformational change of pump protein 5) This protein specific to certain substances to change shape, and only specific substances can pass.
Outline the features of facilitated diffusion of glucose molecules. [3]
1) Transport/carrier protein is used 2) There is specific binding site in protein for glucose to bind 3) Glucose binding causes conformational change in protein 4) No ATP is required 5) Movement is down the concentration gradient.
Explain what is meant by the term hydrolysis of ATP. [2]
1) Using water 2) to break bonds between phosphate groups
Describe the process of exocytosis. [3]
1) Vesicle moves towards cell surface membrane 2) The vesicle fuses with the membrane 3) The contents inside vesicles are released 4) This is active process: ATP is used.
Explain how enzymes that are secreted by cells are packaged into vesicles and exported. [4]
1) Vesicles form from Golgi body 2) Vesicles move to cell membrane 3) Cytoskeleton/microtubules help the movement of these vesicles and ATP is required 4) Vesicles fuses with cell membrane 5) Exocytosis happen and the enzymes are released.
Aquaporins are membrane channel proteins in plant and animal cells. They permit the movement of water across membranes. Explain why they are necessary. [3]
1) Water molecules are polar: few polar molecules pass through the phospholipid bilayer 2) Core of membranes are hydrophobic 3) Channels through aquaporins are hydrophilic; they increase permeability of water 4) Water is important; they are solvent and supports turgidity.
Suggest why 'fluid mosaic' is an appropriate term to use to describe membrane structure. [3]
Fluid: 1) Molecules of membrane move about; they flow 2) Phospholipid and proteins are moving Mosaic: 3) Protein molecules are scattered on their layer 4) There are many different proteins: for example, aquaporins or carrier proteins.
State components of a cell surface membrane other than phospholipid molecules and describe their function.
Glycoprotein 1) Receptor 2) cell recognition 3) cell adhesion Glycolipid 1) Cell adhesion 2) interacts with water to stabilise the membrane Cholesterol 1) Stabilises membrane 2) regulates the fluidity of membrane 3) prevents polar molecules through membrane Protein 1) Receptor 2) enzyme 3) anchoring skeleton 4) cell to cell adhesion 5) channel/carrier allowing facilitated diffusion 6) carrier protein for active transport
Name and describe the process by which calcium ions are moved across the membrane. [3]
Name: Active transport Description: 1) Calcium ions move against their concentration gradient 2) through carrier protein or pump protein 3) Calcium ion combines with the binding site 4) ATP causes carrier protein to charge its shape.
State two similarities and two differences between facilitate diffusion and active transport. [4]
Similarities: 1) They both use carrier proteins 2) They are both specific: they have specific bind place 3) They both involve shape change of protein 4) They both involve the movement of ions/polar molecules. 5) They are both movements across membranes Differences: 1) Facilitated diffusion is the movement down the concentration gradient 2) facilitated diffusion is the passive process: it doesn't require ATP 3) Facilitated diffusion uses different types of protein but active transport only uses carrier proteins.
