B2.2 The Challenges Of Size Flashcards
What is surface area to volume ratio?
Surface area per unit volume
Why is surface area to volume ratio important?
Because diffusion over greater distances does not occur fast enough in order to meet demand of big organisms
How is rate of diffusion maximised in alveoli?
There are a lot of them and they have high surface area so that there can be a capillary network around the alveoli
Give an example of an exchange surface in a transport system
Villi on the walls of the small intestine have high surface area so that more molecules of food can be absorbed by blood
Why are transport systems important?
Transport systems in animals are important to transport toxic waste like urea to kidneys
What is the circulatory system?
A system made of your heart and blood vessels where blood is transported
What is the human circulatory system called?
Double circulatory system as blood flows through the heart twice in one circuit
What are the advantages of a double circulatory system?
Blood can be pumped with higher pressure so that materials are transported quicker
Oxygenated and deoxygenated blood do not mix
Why is blood pumped around the body?
To transport glucose and oxygen which diffuse into cells
To transport CO2 back to the lungs to be removed
What are blood vessels and what are the 3 main types?
Blood vessels are hollow structures which transport blood around the body
Artery, vein, capillary
Describe the structure of arteries
Arteries have a thick outer wall and thick layer of muscle to withstand high pressure. They also have a small lumen to increase pressure
Describe the structure of a vein
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
Describe the structure of capillaries and how they are adapted to their function
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
How is blood pumped through the body and how does pressure changs?
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
What is in blood?
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
Define transpiration
The movement and loss of water through a plants leaf
What is the transpiration stream?
The constant flow of water through roots, through xylem and out from leaves
How does water enter the xylem?
Water diffuses through root hair cells by osmosis and travels from cell to cell until it reaches the xylem
What does the xylem transport?
Water and mineral ions from the soil to the plant through active transport
What does phloem transport?
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.
What is translocation
The movement of sugars from a leaf to their parts of a plant
What is the structure of xylem?
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
What is the structure of phloem?
Living cells
Cell walls have sieve plates which allow sugars to pass through
2 way flow of water and food
What are vascular bundles and how do they provide support?
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
How is water lost from a leaf and carbon dioxide taken in?
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
Where are stomata found and when do they open and close?
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
What is the purpose of the waxy cuticle?
To prevent a lot of water loss and waterproofing
Why do plants wilt?
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
How do you measure the rate of transpiration?
Speed = distance/time
Be careful with units
What 4 factors affect the rate of transpiration?
Anything that affects the rate of photosynthesis Light intensity Temperature Air movement Humidity
How does light intensity and temperature affect rate of transpiration?
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
How does air movement and humidity affect rate of transpiration?
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
What does the blood transport?
Oxygen and glucose needed for respiration and carbon dioxide
