Biology - movement of particles

diffusion definition

the passive and random, net movement of particles from an area of high concentration to low concentration until an equilibrium is reached

osmosis definition

the net, passive and random movement of water from a high water potential to a low water potential across a partially permeable membrane until an equilibrium is reached

active transport definition

movement of particles from an area of low concentration to an area of high concentration until the particles have accumulated - it requires energy in the form of ATP which comes from respiration inside mitochondria

partially permeable

some particles can fit through and some are too large. the cell membrane in animal and plant cells is partially permeable e.g. small molecules can fit, and large molecules cannot fit

net definition

overall effect

equilibrium definition

even spread of particles after diffusion

passive definition

process that does not require extra energy - particles use their natural kinetic energy to move

active definition

process that requires extra energy

turgid definition

when plant cells take in water by osmosis and the water pushes against the cell wall - the cell is firm

flaccid definition

when a plant cell loses water by osmosis, and the cell contents is reduced - the cell is floppy

plasmolysed definition

when a plant cell loses all of its water and the cell membrane comes away from the cell wall

why does diffusion occur

• moving at random due to their kinetic energy

• if you have a high concentration of particles in one area, then this random movement will cause them to spread out

• they will continue to spread out until they are evenly distributed

• we say they have equilibrium

• particles will move at random in all directions but most will move from the area of high concentration to an area of lower concentration

• we say that there is a net movement of particles from the higher to lower concentration

• the difference between the concentrations is the concentration gradient

• there is no energy needed and so the process is passive

rate of diffusion

• the size and mass of the particles

• the concentration gradient - diffusion is the movement from a high to low concentration of molecules

• the temperature

importance of diffusion in living organisms

• nutrients and oxygen diffuse into living cells and waste products like carbon dioxide diffuse out of the cells through the cell membrane

• carbon dioxide for photosynthesis also diffuses into the leaves through openings called stomata

• molecules moving across the placenta e.g. oxygen and glucose

• gas exchange at the lungs

• glucose molecules entering the blood in the small intestine during digestion

Surface area to volume ratio

• oxygen enters a cell by diffusion across the cell membrane

• the more membrane the cell has, the more oxygen can diffuse into it

• this is the cells surface area

• however, the amount of oxygen needed by the cell depends on its volume

• the larger the cell the more oxygen it needs

• the larger this ratio the easier it is for an object, cell or organism to take in or give out chemicals or heat

what types of organisms have a large surface area to volume ratio

single-celled organisms such as amoeba so they can gain enough oxygen by diffusion across its surface

what organisms have a much smaller SA to Vol ratio

large-multi cellular organisms as they can’t get enough oxygen by diffusion across their skin and so they need specialised organ with large surface areas to allow exchange of gases to occur

osmosis in animal cells

animal cells have no cell wall, and so water moving into the cell can cause the cell to burst (or lyse) - this happens when the animal cell is in a dilute solution (hypotonic)

what happens to the animal cell when water moves out of it ?

the cell shrinks (or crenate) and this happens when the animal cell is in concentrated salt/sugar solution

plant cell in distilled water and a concentrated solution

plants cells left in dilute solutions - water moves into the cell, the cell becomes firm or turgid - the cytoplasm and vacuole push against the cell wall

plant cells left in concentration salt'/sugar solutions - water moves out of the cell, the cell becomes floppy or flaccid

plant cells left in very concentrated salt/sugar solutions - so much water moves out of the cell that the cell membrane pulls away from the cell wall - the cell is now plasmolysed

what is the importance of osmosis in plant cells

1. turgor in plant cells provides support to the green parts of plants

2. uptake of water through the root hairs and movement through the root

observing diffusion in gelatine

measure 2cm³ of methylene blue and put it into a boiling tube. take a test tube containing only gelatine, invert it and lower it into the methylene blue. measure 2cm³ of HCl and put it into another boiling tube. take a test tube containing gelatine and universal indicator, invert it and lower it into the boiling tube containing the HCl

results of diffusion in gelatine

methylene blue - diffused a little way up

HCl - red diffused neatly all the way up and then morphs with the green gelatine

demonstrating osmosis in eggs

two raw eggs have had their shells removed by soaking them in acid. this leaves the membrane surrounding the white and yolk in tact. the volume of the eggs will be measured using a displacement can. Egg A will then be put in a beaker of distilled water and Egg B in one of concentrated salt solution

osmosis in eggs results

Egg A will displace more water as the distilled water has a higher water potential and so water will move to the egg. Egg B will displace less water as the egg has a high water potential than the salt solution

investigating the rate of osmosis using visking tubing

visking tubing is a synthetic partially permeable membrane which allows small molecules to pass through but not large molecules. the visking tubing bag contained a sugar solution which was surrounded by pure water. the visking tubing was rinsed after it had been filled up to ensure no sugar solution remained on the outside of the bag

results of visking tubing experiment

the more time left the higher the solution

investigating osmosis in living tissues

label six boiling tubes with each a different concentration of distilled water. use a measuring cylinder to add 20cm³ of correct solution into its boiling tube. use a cork borer to cut 6 potato cylinders and cut off the skin ang cut the lengths to approximately 3cm. find out the mass of a cylinder, record it in the table for 0.0M salt solution and then put the chip in the appropriate tube. repeat for other 5 tubes. leave for at least 24 hours. tip each potato cylinder out of its solution, do not get the cylinders mixed up, pat them dry using tissue paper and measure their mass, recording it in the table. work out the % change in mass for each cylinder

demonstrate plasmolysis in onion epidermis

remove a small square of onion epidermis measuring from the inside of one of the fleshy leaves of onion bulb. using forceps mount this epidermis on a slide and using a pipette add a few drops of water. gently lower a cover slip over the epidermis using a mounting needle. remove any excess water off the slide with filter paper. place the slide on the stage of the microscope and observe with x4, x10 and x20 objective. irrigate the slide by placing a ew drops of concentrated salt solution on one side of the cover slip. place filter paper on the opposite side of the cover slip and soak up the water under the cover slip so that the salt solution is drawn under it

active transport

goes from low to high concentration, against the concentration gradient and requires energy which is provided by respiration and so cells which carry out active transport will contain a lot of mitochondria.