B2.2 The Challenges Of Size

Question 1

What is surface area to volume ratio?

Answer 1

Surface area per unit volume

Question 2

Why is surface area to volume ratio important?

Answer 2

Because diffusion over greater distances does not occur fast enough in order to meet demand of big organisms

Question 3

How is rate of diffusion maximised in alveoli?

Answer 3

There are a lot of them and they have high surface area so that there can be a capillary network around the alveoli

Question 4

Give an example of an exchange surface in a transport system

Answer 4

Villi on the walls of the small intestine have high surface area so that more molecules of food can be absorbed by blood

Question 5

Why are transport systems important?

Answer 5

Transport systems in animals are important to transport toxic waste like urea to kidneys

Question 6

What is the circulatory system?

Answer 6

A system made of your heart and blood vessels where blood is transported

Question 7

What is the human circulatory system called?

Answer 7

Double circulatory system as blood flows through the heart twice in one circuit

Question 8

What are the advantages of a double circulatory system?

Answer 8

Blood can be pumped with higher pressure so that materials are transported quicker

Oxygenated and deoxygenated blood do not mix

Question 9

Why is blood pumped around the body?

Answer 9

To transport glucose and oxygen which diffuse into cells

To transport CO2 back to the lungs to be removed

Question 10

What are blood vessels and what are the 3 main types?

Answer 10

Blood vessels are hollow structures which transport blood around the body

Artery, vein, capillary

Question 11

Describe the structure of arteries

Answer 11

Arteries have a thick outer wall and thick layer of muscle to withstand high pressure. They also have a small lumen to increase pressure

Question 12

Describe the structure of a vein

Answer 12

Veins have a thin outer wall with a thin layer of muscle and fibre. The lumen is large and the veins have valves to stop blood from flowing the wrong way

Question 13

Describe the structure of capillaries and how they are adapted to their function

Answer 13

Capillaries have a very small lumen and made of a 1 cell thick wall. They link arteries and veins to tissue and organs so are present nearly everywhere. Their walls are semipermeable so that substances can diffuse

Question 14

How is blood pumped through the body and how does pressure changs?

Answer 14

Strong contractions of cardiac muscles create waves which caus artery walls to expand and contract which causes blood to move forward

Pressure falls as blood passes into capillaries so thick walls are not required. Valves prevent the back flow of blood

Question 15

What is in blood?

Answer 15

Red blood cells - which carry oxygen and fit through the lumen of a capillary one at a time

White blood cells - large cells with a nucleus used to engulf microorganism and release antibodies

Plasma - contains 90% water and is a straw coloured liquid where many materials are dissolved in for transportation including hormones

Platelets - structures that help blood to clot

Question 16

Define transpiration

Answer 16

The movement and loss of water through a plants leaf

Question 17

What is the transpiration stream?

Answer 17

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

Question 18

How does water enter the xylem?

Answer 18

Water diffuses through root hair cells by osmosis and travels from cell to cell until it reaches the xylem

Question 19

What does the xylem transport?

Answer 19

Water and mineral ions from the soil to the plant through active transport

Question 20

What does phloem transport?

Answer 20

Transports dissolved sugars produced during photosynthesis and water from leaves to other areas of the plant which is called TRANSLOCATION. Sugars are transported to store as energy.

Question 21

What is translocation

Answer 21

The movement of sugars from a leaf to their parts of a plant

Question 22

What is the structure of xylem?

Answer 22

A tube made from dead xylem cells which water and minerals flow through
No cell walls between cells of xylem
Thickened by cellulose and ligin
Transport is one way

Question 23

What is the structure of phloem?

Answer 23

Living cells
Cell walls have sieve plates which allow sugars to pass through
2 way flow of water and food

Question 24

What are vascular bundles and how do they provide support?

Answer 24

Vascular bundles are structures which are packed xylem and phloem tissue which provide support

They form a leaf network to support leaves
They are located in the outer stem to provide strength against wind and bending
Found in roots so that it can bend securely

Question 25

How is water lost from a leaf and carbon dioxide taken in?

Answer 25

Through the stomata on the surface of a leaf cell water evaporates out and carbon dioxide diffuses in. Guard cells allow the stomata to open and close

A concentration gradient is formed between the air inside a leaf and outside so vapour diffuses out into the air
As more water leaves pressure decreases in the xylem tubes so water moves up from below

Question 26

Where are stomata found and when do they open and close?

Answer 26

They are found mainly on the underside of a leaf. When there is plenty of light and water, the guard cells take in water and become turgid which causes the stomata to open.

When guard cells become flaccid and lose water the stomata closes

Question 27

What is the purpose of the waxy cuticle?

Answer 27

To prevent a lot of water loss and waterproofing

Question 28

Why do plants wilt?

Answer 28

If a plant takes in less water than it loses the leaves collapse and wilt. This decreases surface area for photosynthesis and causes the stomata to close

Question 29

How do you measure the rate of transpiration?

Answer 29

Speed = distance/time

Be careful with units

Question 30

What 4 factors affect the rate of transpiration?

Answer 30

Anything that affects the rate of photosynthesis 
Light intensity 
Temperature
Air movement
Humidity

Question 31

How does light intensity and temperature affect rate of transpiration?

Answer 31

Stomata open in light and close in dark so the more light, the more water evaporates. Rate increases until it reaches maximum

Temperature increasing increases the speed of evaporation of water which increases rate

Question 32

How does air movement and humidity affect rate of transpiration?

Answer 32

When air moves over a leaf, more evaporated water vapour moves away from leaf which increases the concentration gradient between the leaf and the air. This increases the rate of diffusion

The higher the humidity, the more water the air contains which decreases the concentration gradient. This decreases the rate of diffusion and therefore transpiration

Question 33

What does the blood transport?

Answer 33

Oxygen and glucose needed for respiration and carbon dioxide