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ALevel AQA Biology, AQA ALEVEL BIOLOGY Exam @ 2023
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ALevel AQA Biology, AQA ALEVELBIOLOGY Exam @ 2023
why is a membrane structure model called a fluid mosaic? - Answer Phospholipids and
proteins are abks to move. And embedded proteins vary in structure and size.
phospholipid bilayer - Answer a double layer of phospholipid molecules that form
membranes in cells. Hydrophilic head and hydrophobic tail forms a hydrophobic region.
Golgi apparatus - Answer modifies and packages proteins for export by the cell
Why is cholesterol important? - Answer Reduces membrane fluidity and permeability
(binds hydrocarbon tails together reducing spaces for diffusion).
Unsaturated membrane - Answer A more liquid membrane as they have kinks in tails so
are more loosely packed.
Saturated membrane - Answer A more solid membrane as they are long and straight so
more tightly packed.
passive transport - Answer the movement of substances across a cell membrane
without the use of energy by the cell
active transport - Answer the movement of materials through a cell membrane using
energy from ATP
Diffusion - Answer Net movement of molecules/ions down a conc. gradient from a
region of high conc. to low conc. through the phospholipid bilayer
facilitated diffusion - Answer Net diffusion down a conc. gradient in which molecules
pass through carrier or channel proteins in c.s.m.
Osmosis - Answer The net movement of water molecules from a region of high water
potential to a region of lower water potential across a partially permeable membrane
(phospholipid bilayer).
carrier protein - Answer a protein that transports substances across a cell membrane
actively or passively.
,Cotransport - Answer Two substances move in the same direction at the same time e.g.
sodium ions and glucose or sodium ions and amino acids.
Rate of diffusion affected by - Answer Temperature, conc. gradient, surface area (due to
microvilli).
Carrier and channel proteins limit rate of diffusion - Answer Number of carrier/channel
proteins becomes a limiting factor as they are limited- eventually working at their
maximum rate.
Rate of facilitated diffusion increased by - Answer Increasing temperature, increasing
conc. gradient, increasing no. Of carrier/channel proteins.
water potential gradient - Answer Maximum value is 0. More solute= lower water
potential (becomes a negative value)
plasmolyzed - Answer shrunken; solute concentration is higher outside (in solution of
lower water potential) the cell cytoplasm. Cytoplasm peels away allowing solutions to
enter (plants). Animal cells shrivel/ crenated.
Lysis of cells - Answer In animals Water enters and cell membrane can not withstand
pressure (no cell wall). Plant cells become turgid.
active transport - Answer Molecules/ions moved across a membrane against their conc.
gradient using specific carrier proteins.
Factors that limit rate of active transport - Answer Number of carrier proteins, lack of
ATP and any factor that reduces aerobic respiration e.g. respiratory poison.
What molecules can cross the phospholipid bilayer (properties)? - Answer Small, non-
polar, lipid soluble and no charge.
What molecules can't cross the phospholipid bilayer (properties)? - Answer Larger,
polar, water soluble and charged.
Eukaryotic cells - Answer Have a membrane bound nucleus, ribosomes and other
membrane bound organelles.
Prokaryotic cells - Answer A cell that lacks a membrane bound nucleus or any other
membrane bound organelles.
Are eukaryotic cells bigger than DNA? - Answer No, prokaryotic cells are much smaller
than eukaryotic cells.
DNA in prokaryotic cells - Answer Circular DNA not associated with proteins.
, DNA in eukaryotic cells - Answer Linear DNA associated with proteins.
binary fission - Answer the division of a prokaryotic cell into two offspring cells, each
having a single copy of circular DNA and variable no. Of plasmids. Produce very large
numbers in a short time (doubles around every 20 mins)
Cytokinesis - Answer Division of the cytoplasm during cell division
Pathogen - Answer a bacterium, virus, or other microorganism that can cause infectious
disease. Pathogen between people not the disease.
Vaccine - Answer Make us immune to disease, but don't stop us from being infected by
pathogens.
Types of foreign cell - Answer Pathogens, abnormal cells e.g cancer cells, transplanted
cells or Toxins. Can be recognised and destroyed by our immune system.
Foreign cells - Answer Recognised due to specific shaped proteins/ glycoproteins on
surface called antigens.
Antigen - Answer A molecule (often a protein/glycoprotein) that triggers an immune
response.
non-specific immune response - Answer Any type of pathogen or foreign cell destroyed.
Immediate response. Involves wbc called phagocytes.
Phagocytosis - Answer process in which phagocytes engulf and digest microorganisms
and cellular debris.
antigen presenting cells - Answer Present antigens from pathogen to specific
lymphocytes called T helped cells.
specific immune response - Answer -humoral immunity/response: B-cells
-cell-mediated/cellular immunity/response: T-cells
Cytotoxic T cells - Answer Seek out and destroy infected body cells by releasing
enzymes that cause lysis of infected cells (hole forms on csm that allows water to
enter).
Agglutination - Answer Clumping together of lots of pathogens, bound together by
antibodies. This mass attracts phagocytes to come and engulf and digest the whole lot.
T helper cells - Answer Activate specific B cells and phagocytes.
Plasma cells produce - Answer antibodies
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