5.4 Active Transport Flashcards
What is active transport?
The movement of molecules or ions into or out of a cell from an area
of low concentration to an area of high concentration (against a
concentration gradient) across a partially permeable membrane.
What does active transport require?
Energy in the form of ATP (from respiration). It is an active process.
A transport/carrier protein in the cell surface membrane which acts like a ‘pump’ and is complementary in shape to the molecule they
transport. Molecules are ‘pumped’ in one direction across the membrane.
Where is active transport important?
– The reabsorption of useful molecules and ions into the blood after
filtration into the kidney tubules.
– The absorption of some products of digestion from the digestive tract.
– The loading of sugar from the photosynthesising cells of leaves into
the phloem tissue for transport around the plant.
– The loading of inorganic ions from the soil into root hairs.
• The uptake of glucose by epithelial cells in the villi of the small intestine.
• The uptake of mineral ions from soil water by root hair cells in plants
How does active transport work?
Active Transport involves the movement of molecules across a membrane using carrier proteins in the Bilayer. These use energy in
the form of ATP to ‘pump’ molecules in one direction across a membrane.
Why do carrier proteins work in active transport?
The carrier Proteins involved in Active Transport are complementary to the
molecule they transport. Once the molecule collides with the Protein, it is transported across the membrane and released the other side. It cannot then be transported back since the carrier Protein is no longer complementary to it.
What is the point of active transport?
Active Transport means that a substance can move against the Concentration Gradient and at a much faster rate than Diffusion alone.
How do molecules move by active transport?
• 1) The molecule or ion binds to receptors (with a complementary
shape) on the carrier protein on the outside of the cell.
• 2) ATP binds to the carrier protein on the inside of the cell. It is
hydrolysed to ADP + P with the release of energy. Phosphate
molecule remains bound to the protein (phosphorylating it).
• 3) This provides the energy required for the carrier protein to
change shape (conformational change).
• 4) The molecule or ion is released to the inside of the cell.
• 5) The phosphate is released from the carrier protein and
recombines with ADP to form ATP.
• 6) The carrier protein returns to it’s original shape.
Factors that affect the rate of active transport
1) The speed of individual carrier proteins – the faster they work, the faster the rate of active transport.
2) The number of carrier proteins – the more carrier proteins present, the faster the rate of active transport.
3) The rate of respiration – release ATP molecules. The more ATP molecules the faster the rate of active transport.
What are the 2 types of bulk transport?
• Exocytosis: the bulk transport of material out of a cell using a vesicle (usually formed from the golgi apparatus) which fuses with the cell surface membrane & the contents are released.
• Endocytosis: the bulk transport of material into a cell by the fusing of a vesicle with the cell surface membrane. There are two types; Phagocytosis (movement of solids), and pinocytosis (movement of liquids)
Why is energy required for bulk transport?
• To transport vesicles to and from the cell surface membrane along the cytoskeleton.
• Fusing the vesicle to the membrane
