Lesson Notes By Weeks and Term v5 - Grade 10

Lesson Video

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Performance objectives

• Describe support systems in plants (turgor, tissues).
• Explain the plant vascular system (xylem, phloem, transpiration).
• Identify three types of animal skeletons (hydrostatic, exo-, endoskeleton).
• Explain the structure and function of the human skeleton.
• Describe blood as a transport medium.

Lesson summary

This week, we delve into the fascinating world of support and transport systems in plants and animals. These systems are essential for life as they provide structural integrity and ensure that vital substances like water, nutrients, and waste are moved efficiently throughout the organism. Understanding these systems allows us to appreciate the complexity and ingenuity of living organisms and how they adapt to their environments. This is particularly relevant in South Africa, where diverse plant and animal life face unique environmental challenges, impacting food security, conservation efforts, and even public health.

Lesson notes

2.1 Support Systems in Plants Plants require support to grow upright and expose their leaves to sunlight for photosynthesis. Unlike animals, plants cannot move to find support, so they rely on various structural adaptations.

Turgor Pressure: This is the pressure exerted by water inside the plant cells against the cell wall. When plant cells are full of water (turgid), they become firm and provide support to the plant. If water is lost (e.g., during drought), turgor pressure decreases, and the plant wilts. Think of a thirsty bunch of spinach wilting in your garden; that's a direct effect of reduced turgor pressure.

Collenchyma: This is a type of plant tissue with thickened cell walls, providing flexible support, particularly in young stems and petioles (leaf stalks). You can find collenchyma in the strings of a celery stalk, allowing it to bend without breaking.

Sclerenchyma: This is another type of plant tissue that provides rigid support. Sclerenchyma cells have heavily thickened cell walls containing lignin, making them very strong. Sclerenchyma cells are often dead at maturity. Examples include the hard shells of nuts and the gritty texture in pear fruits.

Xylem: Although primarily a transport tissue (see below), xylem also contributes significantly to plant support, especially in woody plants. Xylem cells, reinforced with lignin, form the bulk of wood and provide immense structural strength. Think of the massive trunks of baobab trees in Limpopo province. Their strength comes from the highly lignified xylem tissue. 2.2 Transport Systems in Plants Plants need to transport water, minerals, and sugars throughout their bodies. They achieve this through a vascular system consisting of xylem and phloem.

Xylem: Xylem transports water and dissolved minerals from the roots to the rest of the plant. Xylem cells are dead at maturity and form long, continuous tubes. The movement of water in xylem is primarily driven by transpiration, which is the evaporation of water from the leaves.

Transpiration: This process creates a "suction" force that pulls water up the xylem from the roots. Water moves from the soil into the roots by osmosis, then travels up the xylem vessels due to cohesion (water molecules sticking to each other) and adhesion (water molecules sticking to the xylem walls). This is the transpiration stream. The rate of transpiration is affected by factors such as temperature, humidity, wind speed, and light intensity. High temperatures and low humidity increase transpiration.