AQA A LEVEL BIOLOGY Paper 1 2024

AQA A LEVEL BIOLOGY Paper 1 2024 What is the function of the cell membrane? - Correct Answer To control what enters and leaves the cell, acts as a barrier between the cell and its environment. What structural feature of the cell membrane allows substances to enter/leave? - Correct Answer Partially permeable What is the fluid mosaic model? - Correct Answer States that a membrane is a fluid structure (because phospholipids are constantly moving) with a "mosaic" of various proteins embedded in it Describe the structure and function of phospholipids. - Correct Answer Hydrophilic head and hydrophobic tail, arranged in a bilayer (heads face outwards, tails face inwards). Lipid-soluble substances only allowed to pass through. What is the function of cholesterol in the CSM? - Correct Answer Make phospholipids pack more closely together, restricting the movement of the phospholipids, making the membrane less fluid/more rigid. What is simple diffusion? - Correct Answer The (passive) movement of particles from an area of high concentration to an area of low concentration. What is facilitated diffusion? - Correct Answer The passive movement of a large/charged particle down its concentration gradient through a carrier/channel protein. What is the process of facilitated diffusion using a carrier protein? - Correct Answer Large molecule binds to a carrier protein in membrane. Protein changes shape. Protein releases the large molecule on the opposite side of the membrane. What is the process of facilitated diffusion using a channel protein? - Correct Answer Channel proteins form pores in membrane. Charged particles can diffuse down their concentration gradients to the opposite side of the membrane.