biology - active transport across the membrane
What is active transport?
The movement of molecules from a low concentration to a high concentration, using energy from ATP
How is active transport different from diffusion?
Diffusion: moves down the concentration gradient with no energy required
Active transport: moves against the concentration gradient which requires energy
Which part of the cell provides the energy for active transport?
Mitochondria (produces ATP)
whats an example of a substance moved by active transport?
Glucose, ions like Na⁺ and K⁺
Why can’t diffusion do the same job as active transport in some cases?
Diffusion can only move substances down the concentration gradient, so it can’t bring in nutrients if the concentration is already higher inside the cell.
How do carrier proteins “know” which molecule to transport?
They are specific to certain molecules, like a lock and key.
What happens to a carrier protein during active transport?
It binds the molecule, uses energy from ATP to change shape, and releases it on the other side of the membrane.
Why is active transport important in the small intestine?
It absorbs glucose and amino acids from food, even when there’s more inside the cells than in the gut.
Why is active transport essential in nerve cells?
To maintain the sodium-potassium balance needed for nerve impulses.
Can active transport happen without energy?
No – it always requires ATP.
What is the difference between passive and active transport in terms of energy?
Passive = no energy needed;
Active = energy required.
What would happen if a cell couldn’t perform active transport?
It couldn’t take in nutrients efficiently or maintain ion balance, which could stop it from functioning properly.
how does a molecule moves across the membrane during active transport?
The molecule binds to a carrier protein in the membrane.
ATP is used to change the protein’s shape,
which pumps the molecule to the other side of the membrane.
whats two examples of active transport in human cells?
1. Glucose absorption in the small intestine.
2. Sodium-potassium pump in nerve cells (3 Na⁺ out, 2 K⁺ in).
Why is active transport important for cells?
It allows cells to take in nutrients even when there’s more inside the cell than outside, and helps maintain ion balance necessary for proper cell function.
What is osmosis?
The movement of water molecules from a high water concentration to a low water concentration through a partially permeable membrane.
Is osmosis active or passive?
Passive – it does not require energy.
What does “high water concentration to low water concentration” mean in simpler terms?
Water moves from dilute solutions (lots of water, few solutes) to concentrated solutions (less water, more solutes).
Give a biological example of osmosis
Water moving into plant root hair cells from the soil.
What happens to a plant cell in a dilute solution?
Water enters → cell becomes turgid (swollen and firm).
What happens to a plant cell in a concentrated solution?
Water leaves → cell becomes plasmolysed (shrink away from the cell wall).
What happens to animal cells in a dilute solution?
Water enters → cell may burst (lysis) because there’s no cell wall.
What happens to animal cells in a concentrated solution?
Water leaves → cell shrinks (crenation).
How is osmosis different from diffusion?
Diffusion = movement of any substance down its concentration gradient.
Osmosis = only water moves down its water concentration gradient through a partially permeable membrane.
What are cell membranes mainly made of?
Phospholipids, which form a bilayer with hydrophilic heads facing out and hydrophobic tails facing in.
Molecules with hydrophilic heads and hydrophobic tails that form a bilayer, making the membrane partially permeable and helping control what enters and leaves the cell.
What role do proteins play in the membrane?
Proteins in the cell membrane act as channels, carriers, or pumps to help charged particles and larger molecules move in or out of the cell.
How do you answer a cell question? (maths)
Compare the concentration
outside % > inside % (or other way round)
Percentage change in mass
1. final mass - intial mass
2. divide by intial mass
3. 100X (which converts it into percetage)
Say if it increased or decreased (eg. +1%)