Active transport

Explain the process of active transport

1. Molecules move from an area of low concentration to an area of high concentration against the concentration gradient. 2. The protein carrier then changes shape to allow glucose molecules into the cell. This requires energy from the hydrolysis of ATP. The glucose molecules are carried across the membrane in the protein carrier of matching shape. 3. The protein carrier returns passively to original shape to allow more glucose molecules to enter.

State four pieces of evidence for active transport.

1. active transport takes place only in living, respiring cells. 2. the rate of active transport depends on temperature and oxygen concentration. these affect the rate of respiration and so the rate of production of ATP. 3. many cells that are known to carry out a lot of active transport contain very large numbers of mitochondria - the site of aerobic cellular respiration and ATP production. 4. poisons that stop respiration or prevent ATPase from working also stop active transport. for example, cyanide prevents the synthesis of ATP during cellular respiration. it also stops active transport. however, if ATP is added artifically, active transport starts again.

Cells can mantain steep concentration gradients by simply 'mopping up' the substance as soon as it arrives inside the cell. State three ways in which they can do this.

1. by immediately starting to metabolise the substance 2. by chemically changing it to something else 3. or by using a carrier molecule on the surface of an organelle to take it into the organelle

What does active transport involve?

a carrier protein, which often spans the whole membrane

What do both diffusion and facilitated diffusion rely on?

a concentration gradident in the right direction to move a substance into the cell.

What do cells that carry out a lot of active transport generally may have?

a lot of mitochrondria to supply the ATP they need

What type of system is active transport?

a one-way system for each specific substance - this is because the carriers will not transport a substance back through the membrane.

What do the membranes around the organelles and in the cytoplasm provide?

a range of microenvironments within the cell itself, each suited to different functions, such as the protein-packaging systems in the Golgi body

What type of processes are the formation of vesicles and the fusing of vesicles with the surface cell membrane?

active processes, requiring energy supplied by ATP

How does active transport move substances in and out?

active transport can move substances in faster than they can move out by diffusion

What can the system - active transport - in cells enable them to do?

active transport enables them to move substances across membranes against a concentration or electrochemical gradient using energy supplied by the cell.

Explain the importance of active transport in cells

active transport goes against the concentration gradient and so it needs energy to work. it also helps cells to aerobically respire - many cells that are known to carry out a lot of active trasnport contain very large numbers of mitochondria - which is the site of aerobic cellular respiration and ATP production.

What do poisons that stop respiration or prevent ATPase from working, also stop? State an example of this.

active transport. for example, cyanide prevents the synthesis of ATP during cellular respiration. it also stops active transport. however, if ATP is added artifically, active transoport starts again.

In active transport, what is the movement of a substance often linked with?

another particle, such as a sodium ion

How can cells maintain steep concentration gradients?

by simply 'mopping up' the substance as soon as it arrives inside the cell

State an example of when endocytosis occurs at a relatively large scale.

during the ingestion of bacteria during phagocytosis (cell eating).

Suggest how endocytosis and exocytosis provide evidence for the fluid mosaic model of membranes.

during the process of endocytosis, materials can be surrounded by and taken up into membrane-bound vesicles. during the process of exocytosis, a vesicle fuses with the cell surface membrane so the contents are released to the outside of the cell.

State the process in which materials can be surrounded by and taken up into membrane-bound vesicles

endocytosis

What does active transport require?

energy in the form of ATP produced during cellular respiration

Name an example of atime when larger particles need to enter or leave a cell.

for example, when white blood cells ingest bacteria or gland cells secrete large steroid hormones.

State an example of exocytosis in cells.

in cell producing hormones, vesicles containing the hormone fuse with the cell surface membrane to release their contents

What is endocytosis associated with?

intake of materials

Is the carrier protein involved in active transport usually specific?

it may be very specific, picking up only one type of ion or molecule, or it may work for several relatively similar substances that have to compete with it each other for a place on the carrier.

What does the combination of diffusion, facilitated diffusion, and active transport mean for the cell surface membrane?

it means that the cell surface membrane provides control over what moves into or out of the cell

What is phagocytosis associated with?

large particles

What is pinocytosis associated with?

liquids

What is the energy needed for active transport provided by?

molecules for adenosine triphosphate (ATP)

Discuss the role of ATP in active transport in the cell.

molecules of ATP (adenosine trihosphate) provide the energy required for active transport. cells that carry out a lot of active transport generally have any mitochondria to supply the ATP they need. ATP is produced during cellular respiration.

Where does active transport take place in?

only in living, respiring cells

Why must the potassium ions actively moved by the sodium pump, be actively pumped out of the neurone again?

so that another impulse can pass

State the factors in which the rate of active transport depends on. What do these factors affect?

temperature and oxygen concentration. these affect the rate of respiration and so the rate of production of ATP.

What have electron microscope studies shown about pinocytosis?

that pinocytosis is very common as cells take in the extracellular fluid as a source of minerals and nutrients

What direction does an active transport system only move substances in? What is the one exception to this statement.

the direction required by the cell. however, in some cases, they will move out again through open channels - down the concentration or electrochemical gradient that has just been overcome.

What is 'exocytosis'?

the energy-requiring process by which a vesicle fuses with the cell surface membrane so that the contents are released to the outside of the cell.

What does the active transport carrier system in the membrane involve?

the enzyme ATPase

What makes the processes of endocytosis and exocytosis possible?

the fluid mosaic nature of the membrane

What does the membrane have which can enable the movement of larger particles into or out of the cell

the membrane has properties

What is 'endocytosis'?

the movement of large molecules into cells through vesicle formation

What do diffusion and active transport allow?

the movement of small particles across membranes

Define the term 'active transport'

the movement of substances into or out of the cell using ATP produced during cellular respiration

State an example of active transport

the sodium pump that actively moves potassium ions into the cell and sodium ions out

What the sodium pump vital for?

the working of the nervous system - each nerve impulse depends on an influx of sodium ions through the axon membrane.

What type of processes are diffusion and facilitated diffusion? What do these processes allow?

they are passive processes that allow small molecules to move across the membrane.

At what levels can the concentrations of ions and molecules within the cell be?

they can be very different levels from those of the external fluids

What does the enzyme ATPase catalyse?

they hydrolysis of ATP, breaking one bond and forming two more to provide the energy needed by the carrier system in the membrane or to release the transported substances and return the system to normal.

What do many cells that are known to carry out a lot of active transport contain?

very large numbers of mitochondria - the site of aerobic cellular respiration and ATP production

State an example of when endocytosis occurs at a microscopic level.

when tiny amounts of the surrounding fluid are taken into minute vesicles - this process is known as pinocytosis (cell drinking).