Lesson Notes By Weeks and Term v5 - Grade 10

Lesson Video

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Performance objectives

• Describe the three main types of animal skeletons.
• Explain the roles of xylem and phloem in plants.
• Compare open and closed circulatory systems in animals.
• Understand how water moves through tall plants.

Lesson summary

Welcome, Grade 10 Life Sciences learners! This week, we delve into the fascinating world of support and transport systems in plants and animals. Understanding how these systems function is crucial for grasping how organisms survive and thrive in diverse environments, including the unique ecosystems of South Africa. Just think about the baobab tree standing tall in the Limpopo Province, the massive elephants roaming Kruger National Park, or even the crops sustaining our communities – all depend on effective support and transport systems.

Lesson notes

A. Support Systems in Animals Animals need support systems to maintain their shape, protect their organs, and enable movement.

There are three main types: Hydrostatic Skeletons: These rely on fluid pressure to provide support. Muscles contract against the fluid-filled cavity, changing the animal's shape and enabling movement. Think of an earthworm. It doesn't have bones! Instead, it has a fluid-filled body cavity called the coelom. Circular and longitudinal muscles contract against this fluid, allowing it to lengthen, shorten, and move through the soil. Many invertebrates, especially those in aquatic environments, utilize hydrostatic skeletons.

Exoskeletons: These are external, hard coverings that protect the animal. Exoskeletons are made of chitin in arthropods (insects, crustaceans, spiders) or calcium carbonate in molluscs (snails, clams). The exoskeleton provides protection but limits growth. Animals with exoskeletons must periodically shed them (moulting) and grow a new, larger one. Think of a Parktown Prawn (actually a King Cricket). The tough exoskeleton protects it from predators and physical damage. A disadvantage of exoskeletons is that they are heavy, which limits the size of the animal.

Endoskeletons: These are internal skeletons made of bone and cartilage in vertebrates. Bone is a strong, rigid tissue composed of calcium phosphate and collagen. Cartilage is a flexible connective tissue found in joints, ears, and noses. Endoskeletons allow for greater growth and flexibility compared to exoskeletons. Consider a springbok. Its internal skeleton provides support for running and jumping, and the skull protects the brain. The flexible joints, such as the knee and ankle, allow for a wide range of movement.

B. Transport Systems in Plants: Xylem and Phloem Plants need to transport water and nutrients from the roots to the leaves (water and minerals) and from the leaves to other parts of the plant (sugars). This is achieved through two specialized tissues: Xylem: Xylem transports water and dissolved minerals from the roots to the rest of the plant. It's composed of dead cells, namely tracheids and vessel elements, which form continuous tubes. Water moves through the xylem through a combination of: Root Pressure: Water entering the roots creates a pressure that pushes water up the xylem.

However, this is only a minor factor.

Transpiration Pull: The evaporation of water from the leaves (transpiration) creates a tension that pulls water up the xylem. This is the primary driving force for water transport. Think of it like sucking water up a straw. Factors such as high temperatures and dry conditions, common in many South African regions, increase the rate of transpiration. Plants in these areas, such as succulents, have adaptations to minimize water loss.

Capillary Action: The adhesion of water molecules to the xylem walls and the cohesion of water molecules to each other also contribute to water movement.

Phloem: Phloem transports sugars (produced during photosynthesis) from the leaves to other parts of the plant, such as the roots, stems, fruits, and flowers. It's composed of living cells, namely sieve tube elements and companion cells. Sugars are transported in the phloem through a process called translocation. Sugars are actively loaded into the phloem at the source (leaves) and actively unloaded at the sink (roots, fruits, etc.). This creates a pressure gradient that drives the movement of sugars.