Why does oxygen keep on entering an amoeba? Due to a concentration gradient.
Examples of ‘where’ diffusion occurs: Diffusion of CO2 into stomata of leaves during photosynthesis.
Diffusion of: O2 into the alveoli of the lungs CO2 out of capillaries.
The rate of diffusion depends on:1. Concentration the higher the concentration, the faster is the rate of diffusion
The rate of diffusion depends on:2. Temperature the higher the temperature, the faster is the rate of diffusion
The rate of diffusion depends on:3. Size of molecules the smaller the size, the faster is the rate of diffusion
Is the diffusion of water across a semi- permeable membrane from a weak solution to a strong solution. Strong Weak solution solution
Two conditions for osmosis to occur: 1. A semi-permeable membrane.Dilute salt Strong salt or sugar or sugar solution solution 2. A difference in concentration.
Red blood cells are placed in solutions of a different sugar concentration. Explain the result. Sugar molecule Let’s explain each:
RBC & and external solution are at the SAME concentration 1. Water entering RBC = water leaving. What happens? No change in RBC size.
RBC are placed in a very concentrated sugar solution2. RBC are dilute compared to external solution & lose water. What happens? RBC shrink.
RBC are placed in a dilute sugar solution 3. RBC take up water . What happens? RBC swell and finally burst.
Osmosis in plant cellsIn a weak solution In a concentratedwater will enter solution the cellthe cell and fill the loses water andvacuole. The cell goes flaccidmembrane will because thepush against the vacuole becomescell wall making flaccid and thethe cell very cytoplasm stopsinflexible. It is said pushing againstthat cells in this the cell wall. Thisstate are turgid. state is called plasmolysis. 4.9
What happens to PLANT cells?Cell in dilute Cell in same Cell in Cell in a much solution concentrated concentrated becomes: concentration solution solution of solution. becomes: becomes: TURGID FLACCID PLASMOLYSED
Summary: What happens to cells when placed in a solution which is :
Explain why red blood cells burst indistilled water but plant cells do not. Rigid cell wall in plants prevents bursting.
What happens to the cytoplasm in a plasmolysed cell?It is pulled away from the cell wall. A plant wilts when cells are plasmolysed. Is the plant dead in this wilted sate?
What do you expect to happen?Strong sucrose Distilled watersolution in bag. in beaker. Bag membrane Water enters bag by osmosis.
Explain the result of this experiment: 1. Starch is placed inside a bag. 2. The bag is put in a tube containing iodine solution and left for one hour. Iodine molecules diffused into the bag. Bag is selectively permeable.
Explain the results of this experiment Salty water Distilled water1. Slice your potato into 5 mm slices. 2. Place one slice in distilled water and one in salty water.Distilled 3. After 30 minutes, you water can bend the slice of potato in salty water easily. Salty water
Two pieces of celery were for left for 4 hours as shown: Distilled Salty water water Explain the result.
What has happened? Pins mark level of water.Set up apparatus. Result after 1 hour.
Why does water enter an amoeba? An amoeba is more concentrated than thesurrounding water. Water enters by osmosis.H2O
Why doesn’t an amoeba burst like a RBC? Contractile vacuole releases excess water. 2 Excess water enters 1 Water enters contractile vacuole. due to osmosis. 7 The cycle is repeated. 3 Contractile vacuole swells. 6 Contractile vacuole bursts and expels water. 4 Contractile vacuole moves to edge of cell.
Explain why there is no need to place jam in a refrigerator. Bacteria DIE Dilute Bacteria die as theylose water by osmosis. Concentrated
Have a sore throat? Use a salt gargle. WHY is this effective against bacteria? Bacteria die as they lose water by osmosis.
Name the process: Oxygen moves out from a stoma: diffusion Water enters a root hair / amoeba: osmosis
Name the process: Glucose absorbed by small active transport intestine:
Is when substances cross the cell membraneagainst a concentration gradient, usingenergy and carriers in the membrane.
Large molecules and ions pass through proteins in the cell membrane proteins
ATP: Adenosine Triphosphate ATP is the molecule that supplies ENERGY
Fig. 4 Active transport. AGAINST a concentration gradient
How do Osmosis & Diffusion occur? DOWN a concentration gradient Low High conc. conc. AGAINST a concentration gradient
Question: [MAY, 2009] Paper 2Paramecium lives in stagnant water. During aninvestigation about the average time taken by acontractile vacuole to fill up and empty, it wasfound that the contractile vacuoles fill up andempty every 60 seconds when placed in watercompared to 180 seconds when placed in 0.3% saltconcentration. Explain. (4)
Question: [MAY, 2009] Paper 2More water enters a Paramecium living inwater than when is a salt solution. Waterenters the cell by osmosis from a dilute to amore concentrated salt solution. The moreconcentrated the external solution is, the lesswater that enters.
Question: [APRIL, 2010] Paper 2Explain ONE benefit of each of the followingfeatures in the parasitic mode of life of aparasite living in the gut of its host:a) body surface covered with microvilli; (1) To increase the surface area for absorption of food
Question: [APRIL, 2010] Paper 2b) long and thin body; (1) For a large surface area for absorption of food (Accept allows food to flow past so that the parasite is not washed away/decrease in diffusion distance)c) body wall has active transport systems. (1) For uptake of food molecules even against a concentration gradient.
Question: [APRIL, 2010] Paper 1Fresh cherries are fleshy and juicy. Candiedcherries are prepared by placing fresh cherries in avery strong sugar solution. Explain why candiedcherries lose their fleshy juicy texture. (2)
Question: [APRIL, 2010] Paper 1Water moves out of the cherries by osmosis.Cherry cells are dilute when compared to thesurrounding solution. Water follows itsconcentration gradient. Cells become plasmolysed.