Cells & Movement Across Membranes (WJEC GCSE Science (Double Award): Biology): Flashcards

A space in a plant cell containing cell sap, a solution of water and dissolved sugars.

The full vacuole pushes the cell contents outwards against the cell wall, which makes the cell firm.

False.

Animal cells have a cell membrane but no cell wall. Only plant cells have a cell wall.

The nucleus controls the activities of the cell because it contains the chromosomes.

Plants make their own food by photosynthesis, which takes place in chloroplasts. Animals obtain food by eating, so they do not photosynthesise.

The cytoplasm.

Many biological structures, including cells and their sub-cellular structures, are too small to be seen with the naked eye.

A dye used to highlight structures within cells so that more detail can be seen under the microscope.

• Iodine solution is used to stain onion cells

• Methylene blue is used to stain cheek cells

Remove a thin layer of tissue from between the layers of an onion using tweezers.

Place it on a clean slide and add a drop of water.

Add a small drop of iodine stain.

Gently lower a coverslip over the specimen using a mounted needle.

Wipe away any excess water and stain with a paper towel.

So that light passes easily through the sample and individual cells can be clearly seen.

To reduce the risk of squashing the sample and to make air bubbles less likely to form.

A prepared slide is placed onto the microscope stage for viewing.

Use a cotton bud to swab the inside of your cheek.

Swipe the cotton bud across a clean microscope slide.

Add a drop of methylene blue solution.

Gently lower a coverslip using a mounted needle.

Remove excess stain with a paper towel.

• They are plentiful and easy to obtain safely

• They are relatively undifferentiated, so they show the main cell structures

• Use a sharp pencil with clear, single lines and no shading

• Draw only the structures that are visible, in proper proportion

• Use a ruler for label lines, which must not cross and must touch the structure being labelled

False.

Biological drawings use clear single lines with no shading.

True.

Iodine solution can irritate the eyes and skin. Wear eye protection and drench the area with water on contact.

There is a risk of infection being passed to others.

A hazard is something that could harm you, while a risk is the harm that could actually occur.

The process by which a cell develops a structure and internal features that allow it to carry out a specific function.

A cell with a particular structure and internal features that enable it to perform a specific function.

Specialised cells are more efficient at performing specific functions, so the organism can carry out its life processes effectively.

Any three of:

• Nerve cells

• Muscle cells

• Sperm cells

• Red blood cells

As a multicellular organism develops, its cells differentiate to form different types of specialised cell.

A group of similar cells working together to perform the same function.

A group of different tissues working together to perform a specific function.

A group of organs with related functions working together to carry out a particular role.

Cells → tissues → organs → organ systems → organism

Tissues are groups of similar cells that work together to perform the same function.

Any two of:

• Oesophagus

• Stomach

• Small intestine

• Large intestine

• Muscle tissue

• Blood

False.

The heart is an organ. It is made of several different tissues, including muscle and blood.

False.

Cells differentiate so that they become specialised for different functions, giving them different structures.

The movement of substances down a concentration gradient, from an area of higher concentration to an area of lower concentration.

It requires no energy. It happens as a result of the random movement of molecules.

The point at which the concentration of a substance is equal throughout, so there is no further net movement by diffusion.

• Oxygen

• Carbon dioxide

Some substances can diffuse across the membrane while others cannot.

Diffusion is the movement of substances down a concentration gradient.

A non-living, partially permeable material made from cellulose, used to model diffusion across a cell membrane.

Tie off one end of the tubing and fill it with a solution of starch and glucose.

Tie off the other end and place the tubing in a beaker of distilled water. Leave overnight.

Test the contents of the tubing and the beaker for glucose using Benedict's solution and for starch using iodine solution.

Glucose molecules are small enough to diffuse through the pores in the tubing.

Starch molecules are too large to pass through the pores.

The pores are a fixed size. Only particles smaller than the pores can pass through, which is why the membrane is partially permeable.

In the Visking tubing experiment, iodine solution is used to test for the presence of starch.

False.

Diffusion is a passive process and requires no energy.

False.

Visking tubing is non-living. It is made from cellulose and is used as a model of a living membrane.

Visking tubing is non-living, so it cannot carry out the active processes a real cell membrane can. Its pores are also a fixed size, unlike a real membrane.

The perfume particles diffuse from an area of higher concentration to an area of lower concentration until they are evenly distributed.

The movement of water from an area of high water concentration to an area of low water concentration through a selectively permeable membrane.

Osmosis is a special type of diffusion that involves only water molecules moving through a selectively permeable membrane.

A partially permeable membrane.

It has a low water concentration. A concentrated solution contains proportionally less water.

During osmosis, water moves from a dilute solution into a more concentrated one.

Pure water, because it contains no dissolved solute.

Water has moved into the potato tissue by osmosis.

The surrounding solution has a higher water concentration than the potato cell contents.

Water has moved out of the potato tissue by osmosis.

The surrounding solution has a lower water concentration than the potato cell contents.

There has been no net movement of water.

The water concentration inside the potato tissue and in the surrounding solution are equal.

Osmosis involves the movement of water molecules only.

False.

Osmosis is a type of diffusion, so it is a passive process that requires no energy.

False.

Water moves from a high water concentration (low solute) to a low water concentration (high solute).

The movement of molecules across a selectively permeable membrane against a concentration gradient.

From a region of lower concentration to a region of higher concentration, i.e. against the concentration gradient.

Molecules are being moved against a concentration gradient, which does not happen on its own. Energy is needed to drive the movement.

Respiration, which produces the energy-carrying molecule ATP.

• Diffusion moves substances down a concentration gradient; active transport moves them against it

• Diffusion is passive and needs no energy; active transport requires energy from respiration

False.

Active transport is an active process. It requires energy from respiration.

True.

Because active transport works against the concentration gradient, a cell can absorb a substance even when its internal concentration is already higher.

Mitochondria are the site of aerobic respiration, which produces the ATP needed for active transport. Fewer mitochondria means less ATP available.

The selectively permeable cell membrane.

• Diffusion

• Osmosis

• Active transport

A protein made by living cells that acts as a biological catalyst, speeding up the rate of chemical reactions.

A substance that speeds up the rate of a chemical reaction without being changed or used up itself.

• Biological: they are produced by and function inside living cells

• Catalyst: they speed up reactions without being changed or used up

Proteins.

Enzymes are proteins made by living cells that speed up the rate of chemical reactions.

• Building larger molecules from smaller ones

• Breaking down large molecules into smaller ones

They keep the rate of the metabolic reactions needed for life at a suitable level. Without them, reactions would be far too slow to sustain the organism.

False.

Enzymes are not changed or used up. One enzyme molecule can catalyse many reactions.

False.

Enzymes catalyse both the breakdown of large molecules and the building of larger molecules from smaller ones.

Enzymes are proteins made of many amino acids linked together to form a chain, which is then folded into a specific shape.

Each enzyme has a different sequence of amino acids. The sequence determines how the chain folds, and therefore the shape of the enzyme.

An enzyme is a chain of amino acids that is folded into a specific shape.

The amino acid sequence determines the enzyme's structure, because it controls how the chain folds.

The structure determines the shape of the active site, and therefore which substrate the enzyme can act on.

False.

Different enzymes are made from different sequences of amino acids, which is why they fold into different shapes.

The region of an enzyme where the substrate attaches and the reaction takes place.

The molecule that an enzyme acts on, converting it into products.

The shape of the enzyme's active site is complementary to the shape of only that one substrate. No other molecule fits.

The substrate fits precisely into the active site of the enzyme, in the same way that a key fits into a lock.

The shape of an enzyme's active site is complementary to the shape of its substrate.

False.

They are complementary, not identical. They fit together like pieces of a jigsaw, not like two copies of the same piece.

Enzymes and substrates move randomly in solution.

An enzyme collides with its complementary substrate and the reaction occurs.

The product forms and is released from the active site.

The enzyme is unchanged and goes on to catalyse further reactions.

More collisions between enzyme and substrate means a faster rate of reaction and more product.

Fewer collisions means a slower rate of reaction and less product.

It is unchanged and its active site is free to catalyse further reactions.

Enzymes convert substrate molecules into products.

False.

Enzymes are specific. Each enzyme normally acts on only one substrate, because only that substrate is complementary to its active site.

The temporary structure formed when a substrate binds to the active site of an enzyme.

An enzyme and a complementary substrate collide, and the substrate binds to the active site.

Once the enzyme has catalysed the reaction, the products are released and the active site becomes free to form another complex.

When a substrate binds to the active site of an enzyme, an enzyme-substrate complex is formed.

False.

It is temporary. The products are released and the active site is then free to bind another substrate molecule.

Molecules gain kinetic energy, so they move faster and collide more often and with more energy. This means more successful collisions between enzyme and substrate.

The temperature at which an enzyme-controlled reaction occurs at its highest rate.

The optimum temperature for most enzymes in the human body is around 37 °C.

The permanent change in shape of an enzyme's active site, caused by the bonds holding the enzyme together being broken. The substrate can no longer bind.

The bonds holding the enzyme together are broken, so the active site loses its shape.

The substrate can no longer bind because the shapes are no longer complementary. The enzyme has been denatured.

Once an enzyme is denatured it cannot regain its shape, so its activity stops permanently.

Molecules move more slowly, so collisions between enzyme and substrate happen less frequently and with less energy.

False.

Enzymes are not denatured by low temperatures, they simply work slowly. Warming the solution again will increase the rate of reaction.

Boiling is far above the optimum temperature, so it denatures the enzymes. Their active sites lose their shape permanently.

No. The optimum pH varies between enzymes, depending on where in the body they work.

The bonds holding the enzyme together are disrupted or broken.

This changes the shape of the active site, so the substrate can no longer fit and the rate of activity falls. The enzyme is denatured.

An extreme pH breaks the bonds holding an enzyme together, changing the shape of its active site.

False.

A pH that is too far above or below the optimum can also denature an enzyme.

Activity rises as temperature increases towards the optimum.

It peaks at the optimum temperature.

It then falls sharply to zero as the enzyme denatures.

• Temperature

• pH

The breakdown of starch by a carbohydrase enzyme (amylase) into smaller, soluble sugars.

Add starch solution to one test tube and amylase to a second, and place both in a water bath at the chosen temperature for 3 minutes.

Add a drop of iodine to each well of a spotting tile.

Mix the two solutions and start the stopwatch.

Transfer a droplet to a fresh well of iodine immediately, then at 1 minute intervals, recording the colour.

Record the time at which the iodine stops turning blue-black, then repeat at other temperatures.

So that both solutions reach the required temperature before the reaction starts.

A blue-black colour with iodine solution shows that starch is still present.

There is no starch left in the solution. The amylase has broken it all down.

• Independent variable: the temperature of the water bath

• Dependent variable: the time taken for the iodine to stop turning blue-black

Any three of:

• The pH of the solutions

• The concentration of the starch solution

• The volume of starch solution

• The concentration or volume of amylase solution

The less time it takes for the iodine to stop turning blue-black, the faster the rate of reaction.

The iodine takes longer to stop turning blue-black.

There are fewer successful collisions between amylase and starch, so the starch is broken down more slowly.

The amylase has been denatured, so it can no longer bind to the starch or break it down. The starch remains in the solution.

A water bath holds the temperature constant. With a Bunsen burner the temperature may rise above the desired level, so the results are less reliable.

Use a colorimeter to measure the colour of the solution accurately, rather than relying on the eye.

Repeats allow anomalies to be identified and a mean to be calculated, making the results more reliable.

True.

Amylase solution can irritate the eyes and skin. Wear eye protection and wash hands immediately if it comes into contact with them.