Flashcards in Biology Module 3.2 - to be completed, page 79 Deck (24):
How do single-celled organisms get substances they need?
Single-celled organisms can get substances that they need by diffusion across their outer membrane.
Why is it more difficult for a multi-cellular organism to supply all their cells with everything they need through diffusion?
If you're a multi-cellular organism, it would be harder to supply all your cells with everything they need as they're relatively big and have a low surface area to volume ratio and a high metabolic rate (the speed at which chemical reactions take place in the body).
Why do multicellular organisms need a constant, rapid supply of glucose and oxygen?
A lot of multicellular organisms (e.g. mammals) are also very active. This means that a large number of cells are all respiring very quickly, so they need a constant, rapid supply of glucose and oxygen.
What do multicellular organisms need to ensure each cell has a good enough supply of glucose and oxygen?
To make sure every cell gets a good supply, multicellular organisms need a transport system.
What is the transport system in mammals?
In mammals, the transport system is known as the circulatory system, which uses blood to carry glucose and oxygen around the body. It also carries hormones, antibodies (to fight disease) and waste (like CO₂).
What type of circulatory system does a fish have?
A fish has a single circulatory system.
What type of circulatory system does a mammal have?
A mammal has a double circulatory system.
What's the difference between a single and a double circulatory system?
In a single circulatory system, blood only passes through the heart once for each complete circuit of the body.
In a double circulatory system, the blood passes through the heart twice for each complete circuit of the body.
Explain how the single circulatory system in fish works.
In fish, the heart pumps blood to the gills (to pick up oxygen) and then on through the rest of the body (to deliver the oxygen) in a single circuit.
Explain how the double circulatory system in mammals works.
In mammals, the heart is divided down the middle, so it's like two hearts joined together.
1. The right side of the heart pumps blood to the lungs (to pick up oxygen).
2. From the lungs it travels to the left side of the heart, which pumps it to the rest of the body.
3. When blood returns to the heart it returns to the right side again.
Explain how our circulatory system are essentially two linked loops.
Our circulatory system is essentially two linked loops.
One loop sends blood to the lungs -this is called the pulmonary system, and the other sends blood to the rest of the body - this is called the systemic system.
What's an advantage of the mammalian double circulatory system?
An advantage of the mammalian double circulatory system is that the heart can give the blood an extra push between the lungs and the rest of the body. This makes the blood travel faster, so oxygen is delivered to the tissues more quickly.
Do vertebrates have an open or closed circulatory system?
All vertebrates (fish and mammals) have closed circulatory systems - the blood is enclosed inside blood vessels.
How does a closed circulatory system work?
1. The heart pumps blood into arteries. These branch out into millions of capillaries.
2. Substances like oxygen and glucose diffuse from the blood in the capillaries into the body cells, but the blood stays inside the blood vessels as it circulates.
3. Veins take the blood back to the heart.
Do all invertebrates have an open or closed circulatory system?
Neither, some invertebrates (e.g. insects) have an open circulatory system - blood isn't enclosed in blood vessels all the time. Instead, it flows freely through the body cavity.
How does an open circulatory system work?
1. The heart is segmented. It contracts in a wave, starting from the back, pumping the blood into a single main artery.
2. The artery opens up into the body cavity.
3. The blood flows around the insect's organs, gradually making its way back into the heart segments through a series of valves.
The circulatory system supplies the insect's cells with nutrients, and transports things like hormones around the body. It doesn't supply the insect's cells with oxygen though - this is done by a system of tubes called the tracheal system.
What are the five types of blood vessels you need to know about?
The five types of blood vessels you need to know about are: arteries, arterioles, capillaries, venules and veins.
What is role of the arteries and how are they adapted to this role?
Arteries carry blood from the heart to the rest of the body. Their walls are thick and muscular and have elastic tissue to stretch and recoil as much as the heart beats , which helps maintain the high pressure. All arteries carry oxygenated blood to the lungs.
What is the role of the arterioles and how are they adapted to this role?
Arteries branch into arterioles, which are much smaller than arteries. Like arteries, arterioles have a layer of smooth muscle, but they have less elastic tissue. the smooth muscle allows them to expand or contract, thus controlling the amount of blood flowing into tissues.
What is the role of capillaries and how are they adapted to this role?
Arterioles branch into capillaries, which are the smallest of the blood vessels. Substances like glucose and oxygen are exchanged between cells and capillaries, so they're adapted for efficient diffusion e.g. their walls are only one cell thick.
What is the is the role of capillaries and how are they adapted to this role?
Capillaries connect to venules, which have very thin walls that contain some muscle cells. Venules join together to form veins.
What is the role of veins and how are they adapted to this role?
Veins take blood back to the heart under low pressure. They have a wider lumen than equivalent arteries, with very little elastic or muscle tissue. Veins contain valves to stop the blood flowing backwards. Blood flow through the veins is helped by the contraction of the body muscles surrounding them. All veins carry deoxygenated blood, except for the pumolnary veins, which carry oxygenated blood to the heart from the lungs.
What is tissue fluid, and what is it made of?
Tissue fluid is the fluid that surrounds cells in tissues. It;s made from substances that leave the blood plasma, e.g. oxygen, water and nutrients. (Unlike blood, tissue fluid doesn't contain red blood cells or big proteins, because they're too large to be pushed put through the capillary walls.) Cells take in oxygen and nutrients from the tissue fluid, and release metabolic waste into it. In a capillary bed (the network of capillaries in an area of tissue), substances move out of the capillaries, into the tissue fluid, by pressure filtration.