exam questions
Cards (24)
- Describe why single celled organisms do not need a specialised gas exchange surface (2)- They have a large surface area to volume ratio- Therefore, small volume means short diffusion distances to all organelles,- Thus, can rely on simple diffusion, to take in oxygen and remove wastes
- Explain how the structure of the human lungs enables rapid gas exchange (4)- Large SA from the many alveoli- One epithelial cell thick walls of exchange surfaces e.g., capillaries and alveoli creating short diffusion distance- steep concentration gradients maintained by circulation of blood and ventilation- Extensive capillary network around alveoli provides large SA for gas exchange.
- Identify 2 properties that make an efficient exchange system and explain how they affect the rate of gas exchange in the lungs (4)- Alveoli increase the surface area of mammalian lungs- The alveolar wall consists of a single layer of flattened epithelium creating a short diffusion distance- It will allow more gas molecules to diffuse across the gas exchange surface- Thereby increasing the rate of diffusion/gas exchange
- Explain the importance of capillaries in gas exchange (2)- Transports deoxygenated blood high in C02 to the alveoli- Transports oxygenated with low c02 concentration away from the alveoli- This creates a steep concentration gradient for oxygen and c02, facilitating gaseous exchanges 1
- Determine why animal A does not need a circulation system but animal B does (4)- Both have the same volume- However, animal A has a larger surface area thus larger SA: V- So sufficient surface area for diffusion to take place- Distance to cells in centre of A are shorter than for B, allowing quicker diffusion due to shorter diffusion distance.
- Give one function of the glycoproteins found in the cell surface membrane (1)- Act as antigens on the cell surface membrane/ allow cell recognition
- Explain how the structure of a phospholipid molecule contributes to the partial permeability of a cell surface membrane (3)- The phosphate head is polar and fatty acid tails not polar- Allows fat-soluble/non-polar molecules to pass through the membrane- Polar/ionic molecules cannot pass through phospholipid bilayer
- Explain how phospholipids form a cell surface membrane (3)- Hydrophilic parts (polar phosphate head) associates with water- Hydrophobic parts associate with each other but repel water- A bilayer forms with hydrophobic parts pointing in towards the centre and hydrophobic parts on the outside.
- Explain why the phospholipids are arranged in 2 layers in a cell surface membrane (3)- Hydrophilic region (phosphate head) orientated towards water- Hydrophobic region away from water- fatty acid tails- But need the 2 layers as water solution either side of cell membrane
- Describe the structure of the cell surface membrane (3)- Mainly phospholipids and proteins- Phospholipids form a bilayer- Proteins float in the phospholipids and change position- Proteins may be intrinsic or extrinsic
- Explain why plasma membranes are described as fluid mosaic structures (2)- Proteins and phospholipids can move around bilayer via diffusion(fluid)- Membranes contain both proteins and phospholipids which are arranged in a scattered pattern- looks like mosaic.
- State 3 functions of a phospholipid bilayer (3)- Allows cells to maintain different concentration of molecules on either side of the membrane- Enables membrane to fuse with other membranes or to form vesicles- Provides flexibility to the membrane
- Compare and contrast the davson-danielli model of cell surface membrane with the fluid mosaic model (3)- Both contain a phospholipid bilayer- Globular proteins present in both- Membrane proteins in fluid mosaic varied in size whereas the proteins are less varied in size in his model.
- What is the role of cholesterol in cell membranes? (1)- Cholesterol prevents the phospholipid tails from packing too closely together when the temperature decreases to maintain membrane fluidity.
- Explain why betalain molecules cannot move through intact cell membranes (3)- They are too large to fit through the gaps of phospholipids- They are also polar so cannot interact with the non-polar phospholipid tails and can’t move through- Also, no carrier or channel proteins for the belalain molecules to move through.
- Compare and contrast diffusion and active transport (3)- Both move molecules through the phospholipid bilayer- In both molecules can move through proteins- Diffusion occurs down a conc gradient whereas active transport is against conc gradient- Diffusion is passive so does not require ATP whereas active transport does require ATP.
- compare and contrast the processes of endocytosis and exocytosis (3)- both involve the use of vesicles- both involve energy from ATP- endo involved molecules entering cell whereas exo involved molecules leaving the cell- endo involved the formation of new vesicles from the cell surface mem whereas exo involves vesicles fusing with cell mem.
- Explain why ATP is required for the movements of sodium ions into the cell (2)- Because active transport must occur through carrier proteins- Energy is needed to move sodium ions against their concentration gradients
- Describe how glucose moves into the cell (2)- Via carrier protein in cell surface membrane- Glucose moves from high to low concentration- Glucose binds to carrier protein, carrier changed shape to move glucose across membrane
- Describe how glucose moves into cells by facilitated diffusion (2)- Moves in down its conc gradient without ATP- Moves in via carrier
- Give 2 differences between endocytosis and exocytosis (2)- Endocytosis allows substances to move in and exocytosis allows substances to leave the cell.- Exo involves vesicles fusing with the cell membrane whereas endo involves the formation of vesicles from the cell surface mem.
- Describe the function of carrier proteins in a cell surface membrane (4)- Can be used for either facilitated diffusion (from high to low conc) or active transport (against conc gradient)- Moves charged particles into or out of cell- Has 2 shapes and ATP required to change shape of protein and move molecules against conc gradient.
- Describe how glucose enters muscle cells through the cell membrane (2)- Facilitated diffusion- Via carrier proteins located in membrane
- Deduce the effect on increasing the concentration of solution surrounding onion, on the change in mass of the onion (3)- Increased concentration of solution outside, it is stronger (less dilute) than inside of onion- Therefore, water molecules move down the concentration gradient, from an area of low concentration to high concentration across the partially permeable membrane- Water moving out means mass of onion will decrease.