Lesson Notes By Weeks and Term v5 - Grade 10

Lesson Video

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Performance objectives

• Describe the structure and function of xylem and phloem.
• Explain transpiration, translocation, and other plant transport processes.
• Compare open and closed circulatory systems in animals.
• Describe the components and functions of human blood.
• Explain the role of the lymphatic system.

Lesson summary

This week, we delve into the fascinating world of support and transport systems in both plants and animals. Understanding how these systems work is crucial for comprehending how organisms maintain homeostasis and function effectively. In South Africa, this understanding is particularly relevant when considering agricultural practices (irrigation, crop yields), animal husbandry (livestock health), and conservation efforts (understanding the vulnerability of indigenous plant species to drought). Imagine a farmer struggling with wilted crops during a dry season. Knowing how xylem works helps them understand the problem and potentially implement solutions like efficient irrigation techniques.

Lesson notes

2.1 Plant Support and Transport Systems Plants require support to stand upright and transport systems to move water, nutrients, and sugars throughout their bodies. 2.1.1 Support Structures: Cellulose: A major component of plant cell walls, providing rigidity and strength. Think of it as the "brick and mortar" of plant cells.

Turgor Pressure: The pressure exerted by water inside plant cells against the cell wall. This is essential for maintaining plant rigidity. Imagine a deflated balloon vs. an inflated one. A plant cell without enough water is like a deflated balloon, leading to wilting.

Lignin: A complex polymer deposited in the cell walls of some plant cells (especially xylem), making them rigid and waterproof. Think of it as a "reinforcing steel beam" within the plant. Woody plants (trees, shrubs) have a high lignin content. 2.1.2 Transport Systems: Xylem: Transports water and dissolved minerals from the roots to the rest of the plant (unidirectional flow – upwards). Xylem vessels are dead cells, meaning they are hollow tubes made of cell walls. They rely on physical forces for transport.

Phloem: Transports sugars (produced during photosynthesis) from the leaves to other parts of the plant (bidirectional flow – upwards and downwards). Phloem consists of living cells called sieve tube elements connected by sieve plates. These sieve plates have pores allowing sugars to pass through. Companion cells provide metabolic support to the sieve tube elements. 2.1.3 Processes in Plant Transport: Transpiration: The loss of water vapor from the plant leaves through stomata. This creates a "transpiration pull" which helps to draw water up the xylem. Think of it as drinking through a straw – the suction you create pulls the liquid up. Factors affecting transpiration include temperature, humidity, wind, and light intensity. In South Africa, understanding transpiration is vital for managing water usage in agriculture, especially in arid regions like the Karoo.

Translocation: The transport of sugars (sucrose) in the phloem from source (leaves) to sink (roots, fruits, developing buds). This is an active process, requiring energy. The sugars are loaded into the phloem at the source and unloaded at the sink.

Root Pressure: The pressure exerted by the roots that helps push water up the xylem. This is a relatively minor force compared to transpiration pull.

Capillary Action: The ability of water to move up narrow tubes due to cohesion (water molecules sticking to each other) and adhesion (water molecules sticking to the walls of the tube). This contributes to the movement of water up the xylem.

Example 1: Understanding Xylem Function Imagine a tall Eucalyptus tree in the Drakensberg. The roots are deep in the soil, absorbing water. How does that water reach the leaves at the top of the tree, sometimes tens of meters above? The answer is through the xylem. Transpiration from the leaves creates a negative pressure (transpiration pull), which draws water up the xylem vessels. Capillary action and root pressure also contribute, but transpiration pull is the dominant force.

Example 2: Understanding Phloem Function During fruit development in an apple orchard in Elgin, the phloem transports sugars from the leaves (where photosynthesis occurs) to the developing apples. These sugars are used to build the fruit's flesh and provide the sweetness we enjoy. This process of translocation is crucial for fruit production. 2.2 Animal Support and Transport Systems Animals require support to maintain their shape and transport systems to deliver oxygen, nutrients, and hormones, and to remove waste products. 2.2.1 Support Structures: Endoskeletons: Internal skeletons, like those found in vertebrates (including humans and other mammals found in South Africa, like springbok and lions). Bones provide support and protection.

Exoskeletons: External skeletons, like those found in insects and crustaceans (e.g., crayfish found in South African rivers). Exoskeletons provide support and protection but must be shed periodically for growth (molting).

Hydrostatic skeletons: Support provided by fluid pressure within a body cavity, found in some invertebrates like earthworms. 2.2.2 Circulatory Systems: Open Circulatory System: Blood (hemolymph) is not always contained within vessels and flows through sinuses (open spaces) around organs. Found in some invertebrates like insects. Less efficient at delivering oxygen to tissues.

Closed Circulatory System: Blood is always contained within vessels (arteries, veins, and capillaries). Found in vertebrates and some invertebrates. More efficient at delivering oxygen to tissues.

Human Circulatory System: A closed circulatory system consisting of the heart, blood vessels, and blood.

Heart: A muscular organ that pumps blood throughout the body.

It has four chambers: two atria (receiving chambers) and two ventricles (pumping chambers).