Lesson Notes By Weeks and Term v5 - Grade 10

Lesson Video

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Performance objectives

• Describe different animal skeletal systems.
• Explain the function of xylem and phloem in plants.
• Compare open and closed circulatory systems in animals.
• Outline the human circulatory system.
• Explain adaptations in transport systems.

Lesson summary

This week, we delve into the fascinating world of support and transport systems in plants and animals. These systems are crucial for the survival of all multicellular organisms. Without effective support, plants wouldn't be able to reach sunlight for photosynthesis, and animals wouldn't be able to move and maintain their shape. Similarly, transport systems are essential for delivering vital nutrients and removing waste products from every cell. Think about the maize crops that feed many South African families – their ability to stand tall and deliver nutrients to each kernel depends entirely on these systems.

Lesson notes

2.1 Support Systems in Animals Animals require support systems to maintain their shape, protect internal organs, and facilitate movement. There are three main types of skeletal systems: Hydrostatic Skeletons: These rely on fluid pressure within a confined space to provide support. Think of an earthworm; its body cavity is filled with fluid, and muscles contract against this fluid to change its shape and allow it to move. While less common in larger animals, many invertebrates like jellyfish utilize hydrostatic skeletons.

Exoskeletons: These are external, hard coverings that protect the animal. Arthropods (insects, crustaceans) have exoskeletons made of chitin. The exoskeleton provides excellent protection but limits growth. The animal must shed (molt) its exoskeleton periodically and grow a new, larger one. This process makes the animal vulnerable. An example relevant to South Africa is the locust. Its exoskeleton protects it from predators and physical damage, but it must molt to grow.

Endoskeletons: These are internal skeletons made of bone and/or cartilage. Vertebrates (fish, amphibians, reptiles, birds, mammals) have endoskeletons. Endoskeletons allow for greater growth and flexibility compared to exoskeletons. In mammals, bone provides strength and support, while cartilage provides flexibility in joints. Our own skeletons are endoskeletons.

Example: Compare a beetle (exoskeleton) and a springbok (endoskeleton). The beetle's exoskeleton protects it very well, but limits its size. The springbok's endoskeleton allows it to grow much larger and move more quickly, but provides less direct protection than the beetle's exoskeleton. 2.2 Transport Systems in Plants: Xylem and Phloem Plants need to transport water, minerals, and sugars throughout their bodies. They achieve this through two main vascular tissues: Xylem: Xylem transports water and dissolved minerals from the roots to the rest of the plant. Xylem cells are dead at maturity, forming hollow tubes that allow for efficient water transport. Water moves up the xylem through transpiration (evaporation of water from leaves), cohesion (water molecules sticking together), and adhesion (water molecules sticking to the xylem walls). These properties work together to create a "pulling" force that draws water up from the roots. The thick lignin walls provide support to the stem.

Phloem: Phloem transports sugars (produced during photosynthesis) from the leaves to other parts of the plant (e.g., roots, fruits, developing leaves). This process is called translocation. Phloem cells are living, but they rely on companion cells for metabolic support. Sugars are transported in the phloem through a process called pressure flow. Sugars are actively loaded into the phloem, increasing the solute concentration and causing water to move in by osmosis. This increases the pressure at the source (e.g., leaves). At the sink (e.g., roots), sugars are actively unloaded, decreasing the solute concentration and causing water to move out. This decreases the pressure at the sink. The resulting pressure gradient drives the flow of sugars from source to sink.

Example: Imagine a maize plant in a field in the Free State. Water absorbed by the roots travels up the xylem to the leaves. In the leaves, photosynthesis produces sugars that are transported down the phloem to the developing kernels on the cob, providing them with the energy they need to grow. 2.3 Circulatory Systems in Animals Animals have circulatory systems to transport oxygen, nutrients, hormones, and waste products throughout their bodies. There are two main types of circulatory systems: Open Circulatory Systems: In open circulatory systems, blood (more accurately called hemolymph) is pumped by the heart through vessels that empty into open spaces (sinuses) around the organs. Hemolymph bathes the tissues directly. Gas exchange occurs in these open spaces. Open circulatory systems are found in arthropods (insects, crustaceans) and most mollusks. They are less efficient than closed systems because the blood pressure is lower, and it is more difficult to direct blood flow to specific tissues.

Closed Circulatory Systems: In closed circulatory systems, blood is contained within vessels throughout the body. The heart pumps blood through a network of arteries, capillaries, and veins. Capillaries are tiny vessels that allow for the exchange of oxygen, nutrients, and waste products between the blood and the tissues. Closed circulatory systems are found in annelids (earthworms), cephalopods (squid, octopus), and all vertebrates. They are more efficient than open systems because the blood pressure is higher, and it is easier to direct blood flow to specific tissues.

Example: Compare a grasshopper (open circulatory system) and a fish (closed circulatory system). The grasshopper's hemolymph flows freely through its body cavity, making it less efficient at delivering oxygen to its muscles.