Transport In Cells Flashcards
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Active transport
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The transport of molecules against their concentration gradient from a region of low concentration to a region of high concentration
Aerobic respiration
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Respiration that requires oxygen
Agar jelly
A gel made from algae, which provides an ideal growth medium
Amino acid
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The building blocks that make up a protein molecule
Anomaly
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A result that is unusual or unexpected
Blood plasma
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The liquid part of the blood containing useful things like glucose, amino acids, minerals, vitamins (nutrients) and hormones, as well as waste materials such as urea
Boiling tube
Large test tubes made of toughened glass which can be heated on a Bunsen burner
Cell membrane
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A selectively permeable membrane surrounding the cell and controlling the entry and exit of materials
Cell sap
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The liquid transport system of plants, which is mainly water with dissolved salts and sugars
Cell wall
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Outer structure which provides support and prevents the cell from bursting from the uptake of water by osmosis. Plant, fungal and bacterial cell walls have different structures and chemical compositions
Cellulose
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A carbohydrate. It forms the cell wall in plant cells
Concentration
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The concentration of a solution tells us how much of a substance is dissolved in water. The higher the concentration, the more particles of the substance are present
Concentration gradient
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The difference in the concentration of a chemical across a membrane
Diffusion
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The movement of molecules from an area of higher concentration to an area of lower concentration
Humidity
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The amount of water vapour in the atmosphere measured as a percentage
Interpolate
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To estimate unknown values from existing data
Ion
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Electrically charged particle, formed when an atom or molecule gains or loses electrons
Light microscope
Device that uses visible light and a series of lenses to produce an enlarged image of an object
Microorganism
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Microscopic (too small to see) organisms, such as bacteria and viruses
Molecule
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A collection of two or more atoms held together by chemical bonds
Net
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The overall effect of something when all additions and deductions are calculated
Osmosis
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The movement of water molecules across a selectively permeable membrane from a region of higher water concentration to a region of lower water concentration
Partially permiable
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Also called semi-permeable. A partially permeable membrane allows water and other small molecules to pass through, but not larger molecules such as starch
Passive transport
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This is the movement of molecules down a concentration gradient without the need for additional energy, eg diffusion and osmosis
Range
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Range is the difference between the highest and lowest values in a set of data
Root hair cell
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A specialised cell that increases the surface area of the root epidermis to improve the uptake of water and minerals
Solute
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The dissolved substance in a solution
Solution
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Mixture formed by a solute and a solvent
Solvent
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The liquid in which the solute dissolves to form a solution
Sucrose
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A disaccharide made from glucose and fructose. It is used as table sugar
Tissue fluid
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Fluid which is derived from blood plasma that passes through the walls of capillaries
Turgid
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Enlarged and swollen with water. Having turgor. Description of a plant cell in which the vacuole has swollen due to water gain by osmosis
diffusion
Particles in a liquid and a gas move continuously. Because of this movement, particles will spread themselves evenly throughout a liquid or a gas.
If there is a situation where particles of a substance are in a higher concentration, they will therefore move from this region to where they are in a lower concentration. This is called diffusion.
It is important to remember that the particles:
will move in both directions, but there will be a net movement from high to low concentration
will end up evenly spread throughout the liquid or gas but will continue to move
diffusion of coloured chemicals
If a crystal of a coloured chemical, eg potassium manganate(VII), is placed in water, the particles spread out and mix with the water particles. The process is:
1) the potassium manganate(VII) has dissolved
2) the potassium manganate(VII) is the solute
3) the water is the solvent
4) the mixture that results is the solution
The particles have moved from a region of high concentration in the crystal to a low concentration in the water. This difference in concentration is called a concentration gradient. Particles will move down a concentration gradient, from a high concentration to a low concentration.
As well as diffusion occurring between different regions, it also occurs across membranes, between the outside and inside of cells.
The rate of diffusion can be affected by several factors.
1) Concentration gradient:
The greater the difference in concentration, the quicker the rate of diffusion
2) Temperature:
The higher the temperature, the more kinetic energy the particles will have, so they will move and mix more quickly
3) Surface area of the cell membrane separating different regions:
The greater the surface area, the faster the rate of diffusion
Diffusion, surface area and volume
For a bacterium, substances diffuse into and out of the bacterial cell across its surface. Once inside, because of the bacterium’s size, substances will need to diffuse 1 μm or less to where they are needed.
For simple multicellular organisms, such as small plants such as mosses, substances diffuse into the leaves and simple roots over their surface. Again, once inside the plant, they don’t need to move far. Substances move into and around the moss plants by diffusion and osmosis.
Simple organisms therefore take in substances over their body surface. Their needs are determined by their volume. As organisms increase in size, their surface area does not increase at the same rate as their volume. For example, the surface area to volume ratio of a puppy is several times greater than that of an adult dog.
Suggest why puppies are more at risk of losing body heat than adult dogs.
Dogs lose heat over their body surface. Puppies have a larger surface area to volume ratio than adult dogs, so will lose heat more readily.
practical
Investigating the effect of concentration on rate of diffusion
Aim:
To determine if higher concentrations diffuse faster.
Method and risks
Method:
1) Cut a 1 cm3 cube of agar. The agar should be made using 0.1 M sodium hydroxide and coloured with phenolphthalein indicator to produce pink-coloured alkaline agar.
2) Place a 1 cm3 cube of agar into a 0.5 M solution of hydrochloric acid for two minutes.
3) Remove the cube and wash it in water to stop the reaction.
4) Cut the cube in half and measure the distance in millimeters that the acid has caused the agar to become colourless from the outside, inwards towards the centre.
5) Repeat the experiment a further two times and calculate a mean value.
6) Repeat using 1, 1.5 and 2 M solutions of hydrochloric acid.
Risks:
-Hydrochloric acid is corrosive. If it touches skin it should be washed off.
-Goggles should be worn at all times.
Osmosis
Osmosis is the diffusion of water molecules, from a region where they are in higher concentration, to a region where they are in lower concentration, through a partially permeable membrane.
A dilute solution contains a high concentration of water molecules, while a concentrated solution contains a low concentration of water molecules.
Osmosis refers to the movement of water molecules only.
When the concentration of water is the same on both sides of the membrane, the movement of water molecules will be the same in both directions. There will be no net movement of water molecules.
Similar observations will be made with solutions containing different solutes, for instance, salt instead of sugar.
Osmosis across living cells
Cells contain dilute solutions of ions, sugars and amino acids. The cell membrane is partially permeable. Water will move into and out of cells by osmosis.
osmosis in plant cels
Isolated plant cells placed in a dilute solution or water will take in water by osmosis. If the soil is wet or moist then root hair cells will also take up water by osmosis. Leaf cells of land plants, unless it is raining or the humidity is high, will have a tendency to lose water.
Plant cells have a strong cellulose cell wall outside the cell membrane. The cell wall is fully permeable to all molecules. It supports the cell and stops it bursting when it gains water by osmosis.
Under normal circumstances, the cells in all organisms live in a safe equilibrium. They have enough water to live but not too much. They also have the correct amount of salts and sugars. If individual cells are placed in different solutions, we can see how important it is that equilibrium is maintained in living organisms.
osmosis in pure water
In pure water, the cell contents push against the cell wall and the cell becomes turgid. Fully turgid cells support the stems of non-woody plants.
osmosis in a Concentrated solution
In a more concentrated solution, the cell contents lose water by osmosis and the cells shrink. The cell membrance starts to pull away from the cell wall. The cell becomes flaccid.
osmosis in a highly concentrated solution.
definition of plasmolysis.
In a very concentrated solution, the cell membrane pulls away from the cell wall completely; this is plasmolysis.
osmosis in animal cells
Animal cells also take in and lose water by osmosis. They do not have a cell wall, so will change size and shape when put into solutions that are at a different concentration to the cell contents.
In animals, the concentration of body fluids, blood plasma and tissue fluid must be kept within strict limits. If cells lose or gain too much water by osmosis, they do not function efficiently.
eg. Red blood cells lose water and shrink in a concentrated solution. They swell and burst in a solution that is too dilute.
practical - Investigating osmosis in potatoes
Scientists investigate the effects of osmosis on living cells.
- They observe, with a microscope, cells or tissues placed in solutions of different concentration.
- They also measure changes in cylinders or discs of fresh potato or beetroot. Cylinders will have a larger mass than discs, so scientists will have larger measurements to work with.
The following experiment investigates the effect of different concentrations of sucrose on potato tissue. It could also be carried out using salt solution instead of sucrose.
Aims of the experiment:
-To investigate the effect of a range of sucrose solutions on the mass of potato cylinders.
-To determine the concentration of the cell sap of potato cells.
Method and risks
Method:
A 1.0 mol dm^−3 solution of a substance contains one mole of the substance per dm^3.
1) Prepare a range of sucrose solutions eg 0%, 20%, 40% and 100%.
2) Set up a series of boiling tubes with each of these solutions. The 0% sucrose solution will act as the control in the experiment. Make sure each tube is labelled with the concentration.
3) Prepare a blank results table before you begin. Make sure when weighing the potato cylinders, that their masses are not mixed up when recording them. Each cylinder will have a different mass before and after the investigation.
4) Dry a potato strip using a paper towel. Measure the mass of the potato cylinder.
5) Place the potato strip into the 0% solution for 20 minutes.
6) Remove the potato strip, dry it carefully using paper towel. Measure and record the mass of the potato strip.
7) Repeat for each sucrose concentration.
8) For each sucrose concentration, repeat the investigation for several potato cylinders. This allows you to check the precision of your results (results that are close together for the same concentration suggest that the results are precise). The potato cylinders might not all behave in the same way. Making a series of repeat experiments means that any anomalous results can be identified and ignored when a mean is calculated.
Risks:
Make sure that the potato is placed on a ceramic tile when using the cork borer – do not cut the potato cylinders.
Care must be taken when using the scalpel.
Wear eye protection when using chemical solutions.
Rate of water uptake in 1 hour equation
water uptake in 1 hour = change in mass x ((60 minutes) ÷ (length of experiment in minutes))
Rate of water uptake
In this experiment, 0.30 grams of water were taken up by the potato cylinder.
This took place over 20 minutes, so the water uptake in an hour, assuming that the rate was constant, would be:
Water uptake in 1 hour = 0.30 x (60 ÷ 20) = 0.90 grams
The rate of water uptake is therefore 0.90 g h^−1
Percentage change in mass equation
change in mass = ((mass at end - mass at start) ÷ (mass at start)) x 100
For a potato cylinder placed in a sucrose concentration of 0.2 mol dm^−3, the following results were obtained:
Concentration of sucrose %: 0
Mass of potato cylinder at start (g): 2.42
Mass of potato cylinder at end (g): 2.54
Calculate the change in mass as a percentage.
change in mass = ((2.54 - 2.42) ÷ 2.42) x 100 = 5%
Percentiles
Scientists use percentiles to divide a set of data into 100, and look to see where the data lie within these divisions.
The median is the point in a set of data where 50 per cent of the data fall above this value, and 50 per cent below it. This is the 50th percentile.
The 75th percentile is where 75 percent of the data fall below this value.
There are several methods of finding a percentile. The simplest is the nearest rank method. As with finding the median of a set of data, begin by putting the data into order.
percentile ordered rank
ordered rank = (percentile ÷ 100) x number of entries in in data set
This method will only give percentiles as numbers that exist in the data set.
In other methods, percentiles can be interpolated for values that don’t exist in the data set
Active transport
Substances are transported passively down concentration gradients. Often, substances have to be moved from a low to a high concentration against a concentration gradient.
Active transport is a process that is required to move molecules against a concentration gradient. The process requires energy.
Active transport in plants
For plants to take up mineral ions, ions are moved into root hairs, where they are in a higher concentration than in the dilute solutions in the soil. Active transport then occurs to allow the plant to take the nutrients it needs for the soil around it.
Active transport in animals
In animals, glucose molecules have to be moved across the gut wall into the blood. The glucose molecules in the intestine might be in a higher concentration than in the intestinal cells and blood – for instance, after a sugary meal. At this point it will diffuse from high concentration in the intestine to a lower concentration in the blood. This doesn’t require energy.
However, there will be times when glucose concentration in the intestine might be lower. When this is the case, movement of glucose involves active transport. The process requires energy produced by respiration
In animals, plants and microorganisms, substances move into and out of cells by
diffusion, osmosis and active transport.
What is the substances transported by the process of diffusion?
Carbon dioxide, oxygen, water, food substances, wastes, eg urea
What is the substance transported by the process of osmosis?
Water
What is the substances transported by the process of active transport?
Mineral ions into plant roots. Glucose from the gut into intestinal cells, from where it moves into the blood
