Large active animals such as vertebrates and squids have closed circulatory systems (Figure 2.76b). In humans, the circulatory system consists of a muscular pump (the heart) that forces a fluid (blood) through a closed system of tubes (blood vessels), which carry materials rapidly throughout the body. No cell in the body is very far from a blood vessel. Nutrients, wastes and gases exchanged in respiration are carried in the blood. To reach the body cells, materials in the blood must pass into the surrounding body fluid before reaching the cells. (See also Figure 5.24, page 230.)
Fluid from the blood may pass through the blood vessel walls to become part of the interstitial or body fluid which bathes all cells and keeps them moist. Some of this body fluid is reabsorbed in the blood, and the rest drains slowly into other small tubes, the lymphatic vessels.
These join up to form larger vessels which eventually return the fluid they contain, now called lymph, to the blood.
Both the lymphatic system and the blood system are concerned with transporting materials and maintaining the circulation of fluids within the body.
Closed circulatory systems meet the needs of large, active animals.
They provide nutrients and oxygen to cells and carry away wastes and carbon dioxide. However, they use more energy to provide the faster service required.
FIGURE 2.77
Insects have an open circulation system. It consists of a dorsal longitudinal vessel (the heart) that contracts, forcing the fluid out at the anterior end. This fluid flows through tissue spaces and finally re-enters the dorsal vessel through a series of openings. Accessory hearts may help supply fluid to the wings and other distant structures.
The human circulatory system.
(b) (a)
FIGURE 2.76
(a) A simple representation of an open circulatory system.
(b) A simple representation of a closed circulatory system.
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1 Name and describe the roles of three systems used to transport chemicals between the external and internal environments of plants and animals.
2 Identify the gases exchanged in both plants and animals and state the process for which each gas is used.
3 Most organisms require oxygen for respiration. This oxygen is obtained from the environment. Insects, fish, frogs and mammals all have different
structures to facilitate the exchange of gases with the external environment.
a Complete the following table that summarises the structure and function of respiratory systems in different kinds of animals.
b List the features that all respiratory surfaces have in common. Explain how each feature facilitates gaseous exchange.
4 a Label the following diagram of a stomate.
b Describe the role of stomates.
c Explain the mechanism by which stomates open and close.
5 a Define ‘lenticel’.
b Outline the role of lenticels.
6 Explain why multicellular organisms require specialised transport systems.
7 Prepare a cross-sectional diagram of a stem showing the arrangement of xylem and phloem tissue in vascular bundles.
8 Prepare a chart comparing xylem and phloem tissue. Include substances transported, direction of flow and description of the tissues.
9 a Define ‘transpiration’.
b Describe the process of transpiration that occurs in plants from the entry point of water at the root hairs, its route through the plant, to its exit at the stomates.
c Discuss the factors that affect the rate of transpiration.
10 Describe a key difference in the role of the
circulatory system between insects and vertebrates.
11 Compare the efficiency of open and closed circulatory systems.
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1 When we inflate a balloon we push air into it;
when the balloon deflates, air is squeezed out.
Explain how the activity of breathing can be compared with this.
2 The mechanism of gas exchange that occurs at the respiratory surface in all organisms is diffusion.
a Use the diagram of a human alveolus with blood supply to explain why
i oxygen diffuses from the alveolar air into the blood, and
ii carbon dioxide diffuses from the blood into the alveolar air.
b What would you expect to happen to the diffusion rates of oxygen and carbon dioxide for someone breathing into a paper bag?
Explain.
3 Carbon monoxide is a poisonous gas present in cigarette smoke and the exhaust fumes of cars.
Explain why carbon monoxide is dangerous.
4 Study Table 2.7, which illustrates the distribution of stomates on the leaves of different species.
a Suggest an explanation for the distribution of stomates on the lower epidermis of leaves of different species compared with the upper epidermis.
b Consider eucalypt species. Do you think that the distribution of stomates on upper and lower epidermis would follow a similar pattern?
Explain your answer.
5 Water conservation is critical for plants living in arid environments. Research a selected plant species adapted to desert conditions.
a Discuss the distribution and density of stomates.
b What are the consequences of water conservation on gas exchange, the rates of respiration and photosynthesis, and on growth for desert-adapted plants? Explain.
6 It is important not to pile soil or compost around the base of a tree, because it might kill the tree.
Explain why this is so.
7 Marine kelps are large multicellular organisms, yet they do not have specialised transport systems.
Explain why this is so.
8 a Outline a simple experiment you could set up, using a carnation flower and food dye, to test the hypothesis that ‘water travels through xylem in an upward direction’.
b Describe the experimental results that would support the hypothesis. (You will need a microscope for part of this answer.) 9 Research the use of radioactive isotopes in
medicine.
● Make a list of elements that are used.
● For what medical conditions are radioactive isotopes useful?
● How are the isotopes used in the body?
● What can they tell us?
● What, if any, side effects may result from the use of radioactive isotopes?
● Evaluate the advantages and disadvantages of using radioactive isotopes as a diagnostic tool.
capillary
Mitosisis the process by which a multicellular organism grows, repairs, maintains and reproduces itself. It is a type of cell division that results in the production of cells which are identical to the original cell. It really takes place as two separate processes. Mitosis itself is a process of division of the nucleus, and cytokinesis is the division of the cytoplasm.
The nucleus contains inherited structures (chromosomes) that carry the information which controls all the cell’s activities. The single cell from which you developed had 46 chromosomes. In fact, each of your body’s cells has this number of chromosomes. Chromosomes become visible under the light microscope when a cell is about to divide.
Prior to mitosis the original set of 46 chromosomes is copied (duplicated), and in mitosis one copy of each chromosome is distributed to each new cell as it forms. The period when the cells are not dividing is called interphase. During interphase the chromosomes are duplicating, but they are not visible.
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