B2.2- The Challenges Of Size

Question 1

What is a surface area to volume ratio?

Answer 1

The surface area of an object is the total number of all the exterior areas of the object.

E.g. dice
Area of one face x six faces

Volume = length x width x depth

= surface area : volume

Question 2

Why is surface area to volume ratio important?

Answer 2

The larger the organism , the lower the surface area : volume ratio.
Multicellular organisms cannot use simple diffusion to survive, as diffusion over the greater distance cannot occur fast enough.

Question 3

How have multicellular organisms adapted?

Answer 3

Multicellular organisms have developed different adaptations to increase the surface area : volume ratio at exchange surfaces.

E.g. to maximise the rate of diffusion of oxygen into the bloodstream, lungs contain many alveoli , increasing the surface area of lungs.

To maximise the diffusion rate, the walls of the small intestine contain fingerlike villi , increasing the area of the intestine wall .

Question 4

Why are transports needed?

Answer 4

Once a required substance has diffused into the body, it must be transported to where it is needed.

In animals, the circulatory system is the main transport system. The blood carries materials to where they are required.

Plants also have a transport system- xylem tubes carry water and mineral ions around a plant and phloem tubes transport sugars and amino acids.

Question 5

What is the circulatory system?

Answer 5

Your circulatory system is made out of your heart and your blood vessels.

Blood transports substances around your body to the cells that need them, it also carries away waste products.

Question 6

What is a double circulatory system?

Answer 6

Blood flows through the heart twice during each circuit of the body.

The blood that is coloured red is oxygenated blood = high level of oxygen .
The blood that is coloured blue is deoxygenated this means it has low levels of oxygen.

Question 7

How does the double circulatory system work?

Answer 7

Your heart pumps blood to your body organs and tissues. Here oxygen and glucose diffuses out of the blood into the cells.carbon dioxide diffuses out of the cells into the blood. the blood then travels back to the heart which then pumps it to the lungs. in the lungs carbon dioxide diffuses out of the blood to be removed from the body and oxygen diffuses in. The blood returns to the heart and the cycle starts again

Question 8

What are the four main blood vessels?

Answer 8

Pulmonary Vein
Aorta
Vena Cava
Pulmonary artery

Question 9

What are blood vessels?

Answer 9

There are three main types of blood vessels
Arteries
Veins
Capillaries
They are all tubelike substances that transport blood around the body. The hollow cavity in the centre is called the lumen.

Question 10

What is the structure of an artery?

Answer 10

Thick outer wall

Thick layer of muscle and elastic fibres

Small lumen

Smooth lining

Question 11

What is the structure of a vein?

Answer 11

Fairly thin outer wall

Thin-layer of muscle and elastic fibres

Large lumen

Smooth lining

Question 12

What is the structure of a capillary?

Answer 12

Very small lumen

Wall made of a single layer of cells

Question 13

What do arteries do?

Answer 13

Arteries Carry blood away from the heart under high-pressure.

Question 14

What do veins do?

Answer 14

Veins return blood to the heart. They have valves to stop blood flowing the wrong way.

Question 15

What do capillaries do?

Answer 15

Capillaries link arteries and veins in tissues and organs.

The semipermeable walls are only one cell thick, so substances can easily move through them.

Question 16

What is the pulse rate?

Answer 16

When your heart beats, blood is forced into arteries from the ventricles. This makes the artery expand, and then spring back (recoil) when the blood passes. You can feel this as your pulse.

Question 17

What is inside your heart?

Answer 17

Your heart is made of cardiac muscle, only found in the heart.
Cardiac muscle cells are unusual.
The contract without receiving a nerve impulse from your brain.
Many heart muscle cells contract together to produce a heartbeat (70 bpm).

Question 18

Heart diagram description

Answer 18

heart contains four chambers.
two smaller chambers at the top called atria (atrium)
The two larger chambers at the bottom of the ventricles.
Valve separate the chambers.

Question 19

What does the aorta do?

Answer 19

Carries oxygenated blood around the body.

Question 20

What is in blood?

Answer 20

You have 5 L of blood in your body.
Blood is made up of:
Red blood cells
White blood cells
Plasma
Platelets

Question 21

What do red blood cells do?

Answer 21

Small biconcave cells that have no nucleus and contain haemoglobin.
They carry oxygen.
They fit through the lumen of the capillary one cell at a time.

Question 22

What is white blood cells?

Answer 22

Large cells that contain a nucleus.

They fight disease by making antibodies.

Question 23

What is a plasma?

Answer 23

Straw coloured liquid that blood cells float in.
90% of plasma is water.
Many materials are transported (digested food, waste, hormones, antibodies)

Question 24

What is platelets?

Answer 24

Tiny structures that help the blood to clot

Question 25

How does a plant transport materials?

Answer 25

A plant has two transport systems.
One of them is xylem tissues
The second one is phloem tissues.

Question 26

What does xylem tissue do?

Answer 26

Xylem tissue transports water and mineral ions from the roots to the stems, leaves and flowers.
Water diffuses into the root by osmosis.
Mineral ions are taken in by active transport.

Question 27

What do phloem tissues do?

Answer 27

Transports dissolved sugars produced during photosynthesis from the leaves to all other areas of the plant. This is translocation.

Sugars are taken to meristems where they are needed for making new plant cells. This provides an energy store.

Question 28

What is the structure of the xylem?

Answer 28

The xylem vessels are made from dead xylem cells.
There are no cell walls at the end of the cells.
The rest of the xylem cellular cell wall is thickened. This helps to provide support.
One way only

Question 29

What is the structure of the phloem?

Answer 29

Phloem vessels are made of living cells.
The cell walls of the cells do not completely break down.
Instead sieve plates are formed.
The connection of phloem cells effectively forms a tube which allows dissolved sugars to be transported.
It is a two way flow

Question 30

How do vascular bundles provide support?

Answer 30

In the leaf they form a network that supports the softer leaf tissue

In the stem they are located around the outer edge, providing the stand with strength to resist bending in the breeze.

In the root they are found in the centre enabling the route to act as an anchor – the root can vent as the plant moves in the wind.

Question 31

What factors affect the rate of transpiration?

Answer 31

Light intensity
Temperature
Air movement
Humidity

Question 32

How to measure the rate of transpiration?

Answer 32

Rate of movement = distance (mm) / time (s)

Question 33

What is transpiration?

Answer 33

Transpiration is the loss of water from a plant leaves. The water loss must be replaced by uptake through the roots.

Question 34

What is the transpiration stream?

Answer 34

The constant flow of water from the roots, through the xylem and out of the leaves

Question 35

How does water enter the xylem?

Answer 35

Water diffuses from the soil into the root hairs by osmosis

Question 36

How is water lost from leaves?

Answer 36

Stomata on the surface of leaves allow carbon dioxide to diffuse in for photosynthesis.
Guard cells allow the stomata to open and close.
While the stomata are open, water evaporates from cells inside the leaf creating concentration gradient between the air inside the leaf and the surrounding air.
Water vapour then diffuses out of the leaf into the air.

Question 37

Why do plants wilt?

Answer 37

If a plant loses water faster than it takes in, it may wilt. The leaves collapse and droop.

The stomata close, stopping photosynthesis and prevents further water loss.

Plant will remain wilted and will eventually die if it does not receive water.

Question 38

What does a potometer do?

Answer 38

It measures how quickly a plant shoot takes up and loses water.

Question 39

What is the features of alveoli

Answer 39

• large surface area
• thin membrane
• good blood supply
• ventilated