What method is used for small non-polar molecules such as oxygen to move directly through the cell membrane without transport proteins?
Simple diffusion
Occurs through the phospholipid bilayer down a concentration gradient without metabolic energy.
Movement of molecules from a region of higher concentration to lower concentration through membrane proteins without ATP describes which process?
Facilitated diffusion
Uses channel or carrier proteins but still occurs down a concentration gradient.
What process describes the net movement of water molecules across a partially permeable membrane?
Osmosis
Movement occurs from higher to lower water potential through a selectively permeable membrane.
Which process moves substances across membranes against their concentration gradient using energy from ATP?
Active transport
Requires carrier proteins and ATP hydrolysis to move substances from low to high concentration.
What transport mechanism allows two different substances to move across a membrane together using the gradient of one of them?
Co-transport
One molecule moving down its gradient powers the movement of another against its gradient.
True or False:
Channel proteins provide hydrophilic pathways through the membrane for specific ions or polar molecules.
True
Channel proteins form pores allowing passive movement down a concentration gradient.
True or False:
Facilitated diffusion requires ATP hydrolysis to move molecules through membrane proteins.
False
Facilitated diffusion is passive and does not require energy.
Fill in the blank:
The model describing membranes as a flexible layer of phospholipids with embedded proteins is the ______ model.
fluid mosaic
Phospholipids move laterally, and proteins are scattered throughout the membrane.
What molecule present in some membranes restricts phospholipid movement and stabilises membrane structure?
Cholesterol
Reduces membrane fluidity and permeability in animal cell membranes.
What structures within the membrane allow specific ions to pass through by forming hydrophilic pores?
Channel proteins
They enable passive movement of charged particles down electrochemical gradients.
What membrane proteins change shape to move specific molecules across the membrane?
Carrier proteins
Used in facilitated diffusion and active transport.
Which region of the phospholipid molecule forms the hydrophobic interior of the membrane?
Fatty acid tails
These tails repel water and restrict passage of polar molecules.
True or False:
Increasing membrane surface area can increase the rate of transport across the membrane.
True
Larger surface area allows more molecules to cross simultaneously.
What part of the mammalian digestive system absorbs glucose and sodium ions by co-transport?
Ileum
Cells lining the ileum use sodium gradients to absorb glucose efficiently.
What term describes the measure of the tendency of water molecules to move from one region to another?
Water potential
Denoted by Ψ and measured in kilopascals (kPa).
True or False:
Osmosis occurs from a region of lower water potential to higher water potential.
False
Water moves from higher water potential to lower water potential.
Increasing which type of membrane protein would increase the rate of facilitated diffusion?
Channel proteins
More channels increase the number of pathways for molecules to diffuse.
What factor relating to concentration or water potential influences the rate of diffusion across membranes?
Gradient
A steeper gradient increases the rate of movement across membranes.
Fill in the blank:
The breakdown of ______ provides the energy required for active transport.
ATP
ATP hydrolysis releases energy used by carrier proteins to change shape.
What structural adaptation of specialised cells in the gut increases the rate of membrane transport by providing more membrane area?
Microvilli
Found in epithelial cells of the intestine to maximise absorption.
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1: Biological Molecules138
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1: Enzymes & Digestion16
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1: Cell Structure52
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1: Cell Division20
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1: Membranes & Transport20
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2: Exchange & Transport Systems76
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2: Plant Transport20
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2: Immunology36
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3: DNA & Protein Synthesis27
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3: Genetic Diversity14
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3: Biodiversity & Classification32
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3: Investigating Diversity12
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4: Evolution42
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4: Populations & Ecosystems24
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4: Energy & Nutrient Cycles35
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5: Photosynthesis23
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5: Respiration17
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5: ATP & Energy Transfer11
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6: Homeostasis57
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6: Nervous Coordination53
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6: Stimuli & Response62
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6: Muscles14
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7: Inheritance12
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7: Populations (Hardy–Weinberg)15
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8: Gene Mutations & Expression58
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8: Gene Technologies46
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8: Disease24
