Cell Physiology - topic 5

Question 1

what are the 5 ways that substances can enter or leave the cell?

Answer 1

-simple diffusion
-facilitated diffusion
-active transport
-Cytosis
-osmosis

Question 2

what does simple diffusion transport and why?

Answer 2

-non polar molecules e.g. oxygen and carbon dioxide, can pass through the membrane unaided, other very small molecules like water can also pass through unaided due to their very small size
-diffusion is not restricted to just membranes
-diffusion is a passive process and does not require energy

Question 3

what is the definition of simple diffusion?

Answer 3

-diffusion is defined as the net movement of substances from an area of high concentration to an area of low concentration

Question 4

what are the 5 factors that affect the rate of diffusion?

Answer 4

-the greater the concentration gradient the faster the rate of diffusion
-the smaller the molecule the faster the rate of diffusion compared to larger molecules
-diffusion is greater at high temps as it gives the molecules more kinetic energy
-the thickness of exchange surface effects diffusion, the thinner the membranes helps with faster diffusion
-the grater the surface area the faster the rate of diffusion, in some cells the cell surface membrane is extended to increase the area across which diffusion can take place

Question 5

what is the definition of facilitated diffusion?

Answer 5

-this is the type of diffusion when diffusion is supported by protein carriers, that have binding sites that match specific molecules which assist the membrane of molecules across the membrane

Question 6

what are the two types of proteins that are involved in facilitated diffusion?

Answer 6

-carrier proteins which take in molecules, they change shape and release the molecules on the other side of the membrane
-ion channel proteins which allow ions to pass through, come of these are permanently open and some are controlled through a gate

Question 7

what is active transport?

Answer 7

-some molecules and ions need to be moved against the concentration and so energy is required

Question 8

what does active transport involve?

Answer 8

-involves protein carrier molecules, the substance being transported binds to the carrier protein
-the carrier changes shape and releases the transported substance on the other side of the membrane
-the carriers are specific to the particular molecule that it carries

Question 9

why do cells that carry out active transport have many mitochondria?

Answer 9

-they supply the ATP needed for active transport

Question 10

why do root hair cells carry out active transport?

Answer 10

-root hair cells need to take in nutrients to help them grow, there is a high concentration of nutrients inside the root hair cell, compared to a low concentration outside. Therefore active transport is necessary, active transport will stop in water logged soil as there is no oxygen able to get into the cell

Question 11

what happens in the process of cytosis?

Answer 11

-the process of cytosis is important in transporting, large molecules that are too big for the carries and transporting the smaller molecules e.g. water in bulk

Question 12

what are the two types of cytosis?

Answer 12

-endocytosis is the movement of substance into the cell
-exocytosis is the movement of substance out of the cell

Question 13

what happens during endocytosis?

Answer 13

-the cell surface membrane invaginates around substances entering the cell from the outside, this forms a vesicle which then pinches off inside the cell
-when vesicles are taken in the cell the fluid nature of the cell surface membrane allows it to reform and close the gap

Question 14

what are the two types of endocytosis?

Answer 14

-phagocytosis involves the transport of solid matter into the cell
-pinocytosis is the transports liquids into the cell

Question 15

what happens during the process of exocytosis?

Answer 15

-the movement of substances out of the cell
-secretory vesicles move to and fuse with the cell surface membrane, the contents of the vesicles are then released outside the cell, which is then followed by the reforming of the membrane
-exocytosis is important in the secretion of many proteins e.g. digestive enzymes and some hormones

Question 16

what is the definition of osmosis?

Answer 16

-the net movement of water through a selectively permeable membrane, from a solution of less negative water potential to a solution of more negative water potential

Question 17

what do the terms hypotonic, hypertonic and isotonic mean? what happens to both animal and plant cells in these solutions?

Answer 17

-hypertonic is the stronger solution meaning water will move by osmosis from cell cytoplasm into the solution. An animal cells placed in a hypertonic solution will shrink, a plant cell will become plasmolyzed
-hypotonic is the weaker solution meaning water will move by osmosis from solution into cell cytoplasm. An animal cell will burst (cell lysis) in plant cells they will become turgid
-isotonic is when the two solutions are of equal concentration and so osmosis will not occur. All animals cells need to be bathed in isotonic solutions to prevent cell shrinking or bursting

Question 18

what does the water potential of a cell mean? what is it measured in?

Answer 18

-the water potential is the tendency of a cell to take in water by osmosis from pure water across a selectively permeable membrane
-it is measured in kilopascals
-pure water has a water potential of 0KPa as it cannot take in anymore water by osmosis
-water potential is an indication of the free energy of the water molecules, some molecules form hydration shells around the solutes

Question 19

why do solutions always have a negative water potential?

Answer 19

-it will always have some water in hydration shells, the more concentrated a solution is the more negative its water potential is as more water is bound up in hydration shells and are not free
-so it is more likely to take in water by osmosis

Question 20

what does solute potential mean?

Answer 20

-this is the potential of a solution to take in water
-it may be or may not be the same as tendency to take in water known as water potential
-the more solutes that are dissolved in the vacuole of the plant cell the more negative the water potential becomes
-the solute potential is always negative

Question 21

what is the pressure potential of the cell?

Answer 21

-if a plant cell is surrounded by puree water the water potential of the vacuole containing the solutes molecules will be more negative than the surrounding water
-the water will enter the cell by osmosis creating an internal cell pressure which pushes the cell membrane against the cell wall. A turgid cell has a high pressure potential

Question 22

what is the equation to find the water potential of a cell?

Answer 22

-water potential equals the solute potential plus the pressure potential

Question 23

what does the term turgor mean?

Answer 23

-plant cells rely on turgor for support
-the opposing forces of the cell membrane and cell wall on each other help create turgor

Question 24

what does the term flaccid mean?

Answer 24

-if plant tissue suffers a shortage of water, the cells will lose turgor and the tissue is described as being flaccid
- if a large number of cells are flaccid , the phenomenon of wilting occurs

Question 25

what does the term plasmolyzed mean?

Answer 25

-if a plant cell loses too much water by osmosis its vacuole can shrink to the extent that the cell membrane can pull away from the cell wall known as plasmolysis

Question 26

what does the term incipient plasmolysis mean?

Answer 26

-this is the point at which the cell membrane just begins to lose contact with the cell wall