Exchanges across membranes with exam questions


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  • Created by: Shivani
  • Created on: 22-04-11 10:39


Diffusion occurs passively- no ATP is required to move substances across the cell membrane because they move down a concentration graident.

Osmossis is a form of difusion. Osmossis is the movement of water molecules from a region of high concentration to a region of low concentration.

Water potential is the tendency for water to move from one place to another.

Facilitated diffusion:

Channel Proteins are transmembrane proteins that form tunnels through the bilayer for water soluble molecules. Some channels are open all the time other open when triggered by a signalling molecule

Carrier proteins change shape to help move molecules into and out of the cell (use energy from the cell in active transport)

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Active transport

Bulk transport

Exocytosis: substances packaged by the golgi appartus are transported in vesicles out of the cell. The vesicle fuses with the surface membrane and push substances out

Endocytosis: some cells take up large molecules by enclosing them in vesicles or vacuoles formed by the cell surface membrane.

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Exam Questions

Q1. Describe the process of endocytosis

Q2. State three ways in which active transport differs from facilitated diffusion

Q3. Explain why root hair cells have mitochondria

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Q1. Endocytosis is when the cell surface forms vesicles or vacuoles to transport large molecules such as protein through the membrane.

Q2. Active transport uses carrier proteins which use energy in the form of ATP and  moves substances againt their concentration graidient. Whereas facilitated diffustion uses channel protein and does not require ATP

Q3. Root hair cells have mitochondria to provide energy for active transport of ions

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