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Biology

Example output

Processes and structures, with every fact traced back to your page.

Source: biology-ch4.pdf · pages 40–52

Summary

Chapter 4 covers transport across membranes. Diffusion and osmosis are well explained; active transport is introduced but the role of ATP is only mentioned in a figure caption, which is easy to miss when revising from the body text alone.

Passive transport

Diffusion and osmosis, both driven by concentration gradients and requiring no energy.

Active transport

Movement against the gradient using carrier proteins and ATP — the energy requirement is the examinable distinction.

Key terms

Osmosispage 42
Net movement of water across a partially permeable membrane, from high to low water potential.
Active transportpage 47
Movement of substances against a concentration gradient, requiring ATP.
Partially permeablepage 42
A membrane allowing some molecules through while blocking others.
Transport across a membrane
1
Diffusion
High → low concentration. No energy.
2
Osmosis
Water only, across a partially permeable membrane.
3
Active transport
Against the gradient. Needs ATP and carrier proteins.

Flashcards

Does osmosis require energy?
No — it's passive, driven by water potential difference alone.
What distinguishes active transport from diffusion?
It moves substances against the gradient and requires ATP.
What is water potential?
The tendency of water to move from one place to another; pure water is zero.

Practice question

A cell is placed in a solution with lower water potential than its cytoplasm. What happens?

Pick an answer to see the reasoning.

Study plan

  1. 1
    Active transport and the role of ATP
    20 min
  2. 2
    Draw and label a membrane with all three transport types
    20 min
  3. 3
    Practice water potential questions
    15 min

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