Movement In and Out of Cells: Biology 0610 (Cambridge O Level / IGCSE)

A student opens a small bottle of nail varnish remover in one corner of a still, closed classroom with no fans or open windows. Within a few minutes, students sitting on the far side of the room notice the smell, even though the air in the room is not being stirred or blown in any way.

Which statement correctly explains why the vapour particles from the nail varnish remover spread across the room?

Cut flowers are often sold without any water around their stems. If a bunch of flowers is left out of water for several hours, the stems become soft and bend over, and the flowers droop. A florist can often revive a drooping bunch by cutting a fresh end from each stem and standing the stems upright in a container of fresh tap water. Within about an hour, the stems become firm and upright again.

(a) State what is meant by osmosis. [2]

(b) The cell sap inside the stem's cells contains dissolved sugars and other solutes, so it is more concentrated than the tap water in the container. Explain, in terms of osmosis, why standing the stems in tap water makes them firm and upright again. [3]

(c) Instead of tap water, the florist stands a second group of drooping stems in a strong sugar solution, which is more concentrated than the cell sap inside the stem's cells. Predict what would happen to these stems, and explain your prediction in terms of osmosis. [3]

A hydroponics company grows lettuce plants with their roots suspended directly in a nutrient solution. This solution is kept much less concentrated in nitrate ions than the cell sap inside the root hair cells. Despite this, the root hair cells continue to accumulate nitrate ions from the solution, so the concentration difference between the inside of the cells and the solution keeps growing larger over time.

(a) Name the process by which the root hair cells take up nitrate ions against this concentration gradient, and state where the energy for this process comes from. [2]

(b) Explain how the structure of the root hair cell membrane allows nitrate ions to move against their concentration gradient, referring to protein carriers. [3]

(c) Explain why root hair cells contain unusually large numbers of mitochondria, linking your answer to the process described in (a). [3]

A student investigates diffusion using a scent-free blue food dye. She places one drop of the dye at the bottom of four identical tall glass cylinders, each filled with the same depth of still water, and does not stir any of them. Two cylinders are placed in a warm water bath at 40 degrees Celsius, and the other two are placed in a fridge at 4 degrees Celsius. She records the time taken for the coloured dye to become visible at a mark two-thirds of the way up each cylinder.

(a) State the factor being investigated in this experiment, and state one variable that has been kept constant between all four cylinders. [2]

(b) The dye reaches the mark faster in the cylinders in the warm water bath than in the cylinders in the fridge. Explain this result in terms of the movement of the dye particles. [2]

(c) State two factors, other than temperature, that affect the rate of diffusion. For one of these factors, suggest a change to the investigation that would increase the rate at which the dye reaches the mark. [2]

A freshwater aquarium fish is accidentally transferred into a marine (saltwater) aquarium tank. The salt water now surrounding the fish's gill cells is a much more concentrated solution than the cytoplasm inside those cells.

(a) State what is meant by osmosis, referring to water potential in your answer. [2]

(b) State whether the water potential of the salt water surrounding the gill cells is higher or lower than the water potential inside the gill cells. Explain your answer. [2]

(c) Predict what will happen to the gill cells by osmosis, and explain your reasoning in terms of water potential. [2]

(d) Gill cells, unlike plant cells, do not have a cell wall. Suggest why this makes gill cells more vulnerable than plant cells to severe changes in the water potential of their surroundings. [2]

A technician makes two artificial "cells": each is a small bag made from partially permeable membrane, filled with exactly the same volume of a coloured dye solution. Bag X is made into a flat, wide shape, so it has a large membrane surface area. Bag Y is made into a compact, rounded shape, so it has a much smaller membrane surface area. Both bags are placed in separate beakers of plain water at the same temperature, and the dye solution inside each bag has the same starting concentration.

Which statement correctly compares the rate at which the dye diffuses out of the two bags?

A marine biologist studies gill cells taken from a fish. The gill cells continuously accumulate potassium ions from the seawater around them, building up a much higher concentration of potassium ions inside the cells than in the seawater outside. Protein carriers in the cell membrane are responsible for this uptake.

To find out how this uptake works, the biologist adds a poison called sodium cyanide to the seawater. Cyanide blocks respiration inside the mitochondria of a cell but does not damage the cell membrane or the protein carriers themselves. She then compares two separate measurements, made before and after the cyanide is added: the rate at which potassium ions continue to accumulate inside the gill cells, and the rate at which oxygen continues to enter the gill cells from the seawater.

(a) State what is meant by active transport. [2]

(b) Predict and explain the effect of adding the cyanide poison on the uptake of potassium ions into the gill cells. [3]

(c) Predict and explain the effect of adding the cyanide poison on the entry of oxygen into the gill cells, contrasting your answer with part (b). [2]

A student compares two samples of red blood cells. Sample P is mixed with distilled water, which contains no dissolved solutes. Sample Q is mixed with a sodium chloride solution that is much more concentrated than the cytoplasm inside a red blood cell.

(a) State whether the water potential of the distilled water is higher or lower than the water potential of the cytoplasm inside a red blood cell, and explain your answer. [2]

(b) Predict what happens to the red blood cells in sample P, using the term haemolysis in your answer, and explain your prediction in terms of water potential. [3]

(c) Name the process by which the red blood cells in sample Q change, and describe what happens to them. [2]

A student investigates osmosis using potato cylinders. She cuts two identical cylinders of potato tissue, blots each dry with paper towel, and weighs each one. She places cylinder 1 in a beaker of distilled water (0.0 mol/dm3 sucrose solution) and cylinder 2 in a beaker of concentrated sucrose solution (0.8 mol/dm3). After 24 hours, she removes each cylinder, blots it dry again, and reweighs it.

Cylinder 1: initial mass 5.00 g, final mass 5.75 g. Cylinder 2: initial mass 5.00 g, final mass 4.30 g.

(a) Calculate the percentage change in mass of cylinder 1. Show your working. [2]

(b) Calculate the percentage change in mass of cylinder 2. Show your working, and give your answer as a negative value to indicate a decrease. [2]

(c) Explain, in terms of water potential, why cylinder 1 gained mass while cylinder 2 lost mass. [2]

(d) State the term used to describe potato tissue that has gained water and is pressing firmly against its cell walls, and the term used to describe potato tissue that has lost water and is no longer pressing firmly against its cell walls. [2]

In the lungs, oxygen moves from the air inside the alveoli, where its concentration is high, into the blood in the surrounding capillaries, where its concentration is lower, passing across the thin cell membranes of the alveoli and the capillary walls. The cells of the alveoli use no energy from respiration to bring about this movement of oxygen.

Which term correctly describes this movement of oxygen from the alveoli into the blood?