The Challenges of Size (OCR GCSE Combined Science A (Gateway): Biology): Flashcards

The rate increases, because substances have less far to travel.

As an organism gets bigger its surface area to volume ratio decreases.

A capillary wall is only one cell thick, giving a short diffusion distance.

False.

Larger organisms have a smaller SA:V ratio. This is a very common mistake.

True.

Its long extension increases the surface area for absorbing water and mineral ions.

To take in what it needs for its life processes and to remove waste that would otherwise build up.

For aerobic respiration, which transfers the energy they need.

For transport of substances and for the many chemical reactions that take place in cells.

To release energy in respiration, and to provide materials for growth and cell repair.

They are needed in small amounts to help the organism use other nutrients efficiently.

Carbon dioxide, which they need for photosynthesis.

Carbon dioxide and urea.

They are toxic, so a build-up would harm the organism.

The cell membrane.

Diffusion, osmosis and active transport.

Both carbon dioxide and oxygen are exchanged, because plants respire as well as photosynthesise.

Urea is a waste substance that must be removed from the body.

Unicellular organisms such as amoeba need no transport system because of their large surface area to volume ratio.

False.

Carbon dioxide is exchanged too — taken in by plants for photosynthesis and released as a waste product of respiration.

False.

Its surface area to volume ratio is large enough for diffusion alone to meet its needs.

The left atrium and the right atrium.

The left ventricle and the right ventricle.

The tricuspid valve.

The bicuspid valve (also called the mitral valve).

The semilunar valves, in the pulmonary artery and the aorta.

They prevent blood flowing backwards, keeping it moving in one direction.

The vena cava, which empties into the right atrium.

The pulmonary vein, which empties into the left atrium.

The pulmonary artery, leaving the right ventricle.

The aorta, leaving the left ventricle.

The right side pumps blood to the lungs.

The left side pumps blood to the rest of the body.

Two joined circuits — one from the heart to the lungs and back, and one from the heart to the body and back.

Blood loses pressure passing through the lungs.

Returning it to the heart lets the pressure be raised again, so the body is supplied quickly with oxygen.

The heart pumps deoxygenated blood to the lungs, where oxygen is taken up and carbon dioxide is released.

It contracts continuously without tiring, and its many mitochondria supply the ATP this needs.

The coronary arteries, which branch off the aorta.

Blood is carried away from the heart in arteries and back towards the heart in veins.

As an artery passes through an organ it narrows into a network of capillaries.

False.

The right ventricle pumps to the lungs. The left ventricle pumps to the rest of the body.

False.

The pulmonary artery carries deoxygenated blood. Arteries are defined by carrying blood away from the heart.

Arteries, veins and capillaries.

Away from the heart.

Towards the heart.

To withstand the high pressure of blood leaving the heart, and to recoil and keep that pressure up.

It helps maintain the high blood pressure.

The blood inside them is at low pressure, so thick walls are not needed.

It reduces resistance to blood flowing at low pressure.

To prevent the backflow of blood, which is at low pressure.

One cell thick.

Being one cell thick gives a very short diffusion distance, so substances pass in and out easily.

To exchange substances with the tissues — delivering oxygen and nutrients and taking away waste.

An artery has a narrow lumen and thick walls.

A vein has a wide lumen and thin walls.

Blood in an artery is at higher pressure than blood in a vein.

Valves in veins stop the blood from flowing backwards.

False.

The blood pressure in arteries is high enough to keep blood moving forwards, so valves are not needed.

True.

The slow flow gives more time for substances to be exchanged with the tissues.

To act as a transport system, carrying useful substances to every cell and waste substances away from them.

To carry oxygen from the lungs to cells throughout the body.

Its biconcave disc shape gives a large surface area to volume ratio, so oxygen diffuses in and out quickly.

It leaves more room for haemoglobin, so the cell can carry more oxygen.

The red protein in red blood cells that binds to oxygen to form oxyhaemoglobin.

Being small and flexible lets it squeeze through narrow capillaries.

The straw-coloured liquid part of blood, in which the blood cells and dissolved substances are carried.

Red blood cells, white blood cells and platelets.

Carbon dioxide, dissolved food molecules and urea.

Water, mineral ions, hormones and antibodies are also carried.

It is the waste product of respiration and must be taken to the lungs to be removed.

Plasma carries heat energy from active organs to cooler parts of the body, such as the hands and feet.

The plasma.

Oxygen binds to haemoglobin in a red blood cell to form oxyhaemoglobin.

The biconcave disc shape of a red blood cell increases its surface area for gas exchange.

False.

They lose their nucleus, leaving more space for haemoglobin.

False.

It also carries dissolved substances such as carbon dioxide, food molecules, urea, hormones and antibodies.

The roots, and in particular the root hair cells.

A single-celled extension of a root epidermis cell that absorbs water and mineral ions from the soil.

It is long and thin, so it reaches between soil particles.

This gives a very large surface area to volume ratio for uptake.

Osmosis.

Dissolved minerals and sugars give the cytoplasm a low water potential.

Soil water has a higher water potential, so water moves in.

Active transport.

They are more concentrated inside the cell than in the soil, so they must move against the concentration gradient, which needs energy.

Together they hugely increase the surface area available for absorbing water and mineral ions.

The roots, the stem and the leaves.

The xylem.

Water enters a root hair cell by osmosis, moving down a water potential gradient.

Root hair cells are extensions of the epidermis cells of the root.

False.

Water enters by osmosis, but mineral ions enter by active transport.

True.

That is why water moves into it by osmosis.

The loss of water from a plant by evaporation and diffusion, mainly from the leaves.

The continuous movement of water up the xylem from the roots to the leaves, replacing water lost by transpiration.

In one direction only — from the roots up to the leaves.

It is a side effect of gas exchange: the stomata must open to let carbon dioxide in for photosynthesis, and water is lost through them.

A tiny pore in a leaf, formed by two guard cells, that allows gases in and out.

They open and close the stomatal pore, controlling gas exchange and water loss.

When water is plentiful they take in water by osmosis and become turgid.

Their uneven cell walls make them curve apart, opening the pore.

When water is short they lose water by osmosis and become flaccid, pulling together and closing the pore.

No photosynthesis is happening, so closing them conserves water.

The transport of dissolved sugars (mainly sucrose) and amino acids through the phloem.

Both up and down the plant, from where substances are made to where they are used or stored.

Transpiration moves water up the xylem in one direction only.

Translocation moves sugars and amino acids through the phloem in both directions.

It requires energy from the plant.

Water is lost from the leaves by evaporation and diffusion through the stomata.

The main sugar transported in the phloem during translocation is sucrose.

True.

They take in water by osmosis, curve apart and open the stomatal pore.

False.

Sugars travel in the phloem. The xylem carries water and mineral ions.

Water and mineral ions, from the roots up to the stem and leaves.

Dissolved sugars (mainly sucrose) and amino acids.

It is made of dead cells joined end to end with no end walls.

This forms a continuous hollow tube that water flows up freely.

It strengthens the cell walls, making them stiff and waterproof, so the tube supports the plant and does not collapse.

Dead — the cell contents are lost, leaving a hollow tube.

Sieve tube elements, joined end to end in columns.

Its holes let sugars and amino acids flow easily from one cell to the next.

It carries out the living functions for the sieve tube element, which has no nucleus of its own.

Living — which is why they need companion cells to support them.

Xylem is made of dead cells with no end walls; phloem is made of living cells with sieve plates.

Xylem is strengthened with lignin; phloem is not.

Vascular bundles.

Xylem cell walls are strengthened by a woody material called lignin.

Sieve tube elements have no nucleus, so they rely on companion cells.

False.

Water moves in one direction only, from the roots to the leaves.

True.

Unlike xylem, phloem is made of living cells, supported by companion cells.

Light intensity, air movement and temperature.

It increases the rate.

More stomata open in bright light, to let carbon dioxide in for photosynthesis.

More open stomata mean more water is lost, so more is drawn up to replace it.

It increases the rate.

Wind blows away the water vapour gathered outside the stomata.

This keeps a steep concentration gradient, so water diffuses out faster.

A higher temperature increases the rate.

Water molecules gain more kinetic energy, so they evaporate and diffuse out of the leaf faster.

Water lost from the leaves must be replaced, so more is drawn up the xylem from the roots.

It is at its lowest — all three factors are reducing the rate of water loss from the leaves.

Almost all the water taken up replaces water lost from the leaves, so uptake is a good measure of the rate of loss.

As light intensity increases, the rate of water uptake by a plant increases.

Moving air increases water loss by removing water vapour from around the stomata.

True.

Most stomata close in the dark, so less water is lost and less is taken up.

False.

Moving air increases the rate, by keeping the concentration gradient steep.