Lesson Notes By Weeks and Term v5 - Grade 10

Lesson Video

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Performance objectives

• Describe xylem and phloem structure and function in plants.
• Explain transpiration, translocation, and root pressure.
• Describe the human circulatory system (heart, vessels, blood).
• Explain the mechanism of blood clotting.
• Compare transport systems in plants and animals.

Lesson summary

This week, we delve into the fascinating world of support and transport systems in both plants and animals. Understanding these systems is crucial because they are fundamental to the survival and function of all living organisms. Imagine a tall baobab tree without its robust support system, or a human being without a circulatory system to deliver oxygen – life as we know it would be impossible. These systems ensure that resources (like water, nutrients, and gases) are distributed effectively, and waste products are removed. Consider the impact of drought on South African agriculture; understanding plant transport systems helps us develop strategies to mitigate its effects.

Lesson notes

2.1 Support and Transport in Plants Plants require support to maintain their structure and expose their leaves to sunlight for photosynthesis. They also need transport systems to move water, nutrients, and sugars throughout their bodies. 2.1.1 Support in Plants: Turgor Pressure: In herbaceous (non-woody) plants, turgor pressure provides support. When plant cells absorb water, their vacuoles fill up, pushing the cytoplasm against the cell wall. This pressure makes the cells rigid, giving the plant its upright form. If water is scarce, turgor pressure decreases, and the plant wilts. Think of a spinach leaf that wilts when you forget to water it.

Cellulose and Lignin: Woody plants rely on cellulose (a carbohydrate) and lignin (a complex polymer) in their cell walls for support. Lignin makes the cell walls rigid and strong, allowing trees to grow tall. Imagine the sturdy trunk of a Mopani tree; its strength comes from lignin. 2.1.2 Transport in Plants: Xylem: Xylem is a vascular tissue that transports water and dissolved minerals from the roots to the rest of the plant. Xylem consists of dead cells called tracheids and vessel elements.

Tracheids: Long, thin cells with tapered ends. Water moves between tracheids through pits (small openings in the cell walls).

Vessel Elements: Wider and shorter than tracheids. They are joined end-to-end to form continuous tubes called vessels. The end walls between vessel elements have perforations (holes), allowing water to flow freely.

Xylem Structure and Function: The dead, hollow structure of xylem vessels and tracheids allows for efficient water transport. The lignified walls provide strength and prevent the vessels from collapsing under pressure.

Phloem: Phloem is a vascular tissue that transports sugars (produced during photosynthesis) from the leaves to other parts of the plant, such as roots, stems, and fruits. This process is called translocation. Phloem consists of living cells called sieve tube elements and companion cells.

Sieve Tube Elements: Long, cylindrical cells that are joined end-to-end to form sieve tubes. The end walls between sieve tube elements are called sieve plates, which have pores that allow cytoplasm and dissolved sugars to pass through. Sieve tube elements lack a nucleus and other major organelles.

Companion Cells: Located alongside sieve tube elements. They contain a nucleus and other organelles and provide metabolic support to the sieve tube elements.

Phloem Structure and Function: The sieve tubes allow for the transport of sugars. The companion cells regulate the flow of sugars and provide energy to the sieve tube elements.

Transpiration: The loss of water vapor from the leaves of a plant. This creates a "pull" that draws water up the xylem from the roots. Several factors affect transpiration rate, including: Temperature: Higher temperature increases transpiration.

Humidity: Higher humidity decreases transpiration.

Wind: Wind increases transpiration.

Light intensity: Higher light intensity increases transpiration (because stomata open for photosynthesis).

Translocation: The movement of sugars from source (e.g., leaves) to sink (e.g., roots, fruits). Sugars are actively transported into the phloem at the source, which increases the water potential in the phloem and causes water to enter from the xylem by osmosis. This creates a pressure gradient that drives the flow of sugars to the sink, where sugars are actively transported out of the phloem.

Root Pressure: The pressure exerted by the roots that helps to push water up the xylem. Root pressure is caused by the active transport of minerals into the root cells, which draws water into the roots by osmosis. Root pressure is generally less important than transpiration pull in most plants, especially tall trees.