Lesson Notes By Weeks and Term v5 - Grade 10

Lesson Video

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Performance objectives

• Describe plant tissues for support and transport.
• Explain water uptake and transport in plants.
• Describe the functions of xylem and phloem.
• Identify components of the human circulatory system.
• Explain the functions of blood components.

Lesson summary

In Week 9, we delve into the fascinating world of support and transport systems in both plants and animals. These systems are crucial for survival, allowing organisms to obtain vital resources and maintain their structure. Understanding these systems is important for understanding how organisms function as a whole. Think about the towering trees in the Kruger National Park or the swift movements of a Springbok; their structure and survival rely on efficient support and transport. In the South African context, where diverse ecosystems thrive, comprehending these processes helps us appreciate and conserve our natural heritage.

Lesson notes

2.1 Support Systems in Plants Plants need support to grow upright and expose their leaves to sunlight for photosynthesis.

They achieve this through: Cellulose Cell Walls: Plant cells have rigid cell walls made of cellulose, providing basic structural support.

Turgor Pressure: When plant cells absorb water, the vacuole swells, pressing against the cell wall. This turgor pressure makes the plant cells firm and contributes to overall rigidity.

Supporting Tissues: Collenchyma: Found in young stems and leaf stalks, collenchyma cells have unevenly thickened cell walls, providing flexible support. Think of celery stalks; they bend but don't easily break.

Sclerenchyma: These cells have very thick, lignified (containing lignin, a strengthening polymer) cell walls, providing rigid support. Sclereids (stone cells) are a type of sclerenchyma, found in pear fruits, giving them a gritty texture. Fibres are another type, found in flax and hemp, used for making ropes and fabrics.

Woody Tissue (Xylem): In older stems and tree trunks, xylem tissue becomes woody, providing significant structural support due to the deposition of lignin. This allows trees to grow tall and withstand strong winds, a common challenge in many parts of South Africa. 2.2 Transport Systems in Plants Plants need to transport water, minerals, and sugars throughout their bodies.

This is achieved through vascular tissues: Xylem: Transports water and dissolved minerals from the roots to the leaves. Xylem is made of dead cells – tracheids and vessel elements – forming continuous tubes. The walls of these cells are strengthened by lignin. Water movement is primarily driven by transpiration (the evaporation of water from leaves), creating a "pull" or tension that draws water up the xylem. This is known as the cohesion-tension theory. Water molecules are cohesive (attracted to each other) and adhesive (attracted to the xylem walls), allowing them to be pulled up as a continuous column. Root pressure can also contribute to water movement, especially at night, but its role is less significant than transpiration pull. Root pressure is due to the active absorption of ions into the roots, creating a water potential gradient that draws water into the xylem.

Phloem: Transports sugars (produced during photosynthesis) from the leaves to other parts of the plant (roots, stems, fruits, and flowers). Phloem is made of living cells – sieve tube elements and companion cells. Sieve tube elements are connected end-to-end, forming sieve tubes. Sieve plates (perforated end walls) allow the passage of sugars. Companion cells support the sieve tube elements. Sugar transport is driven by a process called translocation. Sugars are actively loaded into the phloem at the source (leaves) and actively unloaded at the sink (roots, fruits). This creates a pressure gradient that drives the movement of sugars through the phloem. This is known as the pressure-flow hypothesis.

Example of water transport: Imagine a tall Eucalyptus tree in Mpumalanga. Water is absorbed from the soil by the roots, moves into the xylem, and is pulled upwards due to transpiration from the leaves. The cohesion and adhesion properties of water help to maintain a continuous water column within the xylem vessels. 2.3 Support Systems in Animals Animals have diverse support systems, depending on their body size and habitat.

Invertebrates: Exoskeletons: Insects, such as locusts common in South Africa, have exoskeletons made of chitin, a tough polysaccharide. The exoskeleton provides protection and support but must be shed and replaced as the animal grows (molting).

Hydrostatic Skeletons: Earthworms use fluid-filled cavities and muscles to provide support and movement.

Vertebrates: Endoskeletons: Vertebrates, including humans and other mammals found in South Africa, have endoskeletons made of bone and cartilage.

Bones: Provide support, protect internal organs, and serve as attachment points for muscles.

Cartilage: Provides flexible support, found in joints, ears, and nose.

Joints: Where two or more bones meet, allowing for movement. 2.4 Transport Systems in Animals (Human Circulatory System) The human circulatory system is responsible for transporting oxygen, nutrients, hormones, and waste products throughout the body.

The Heart: A muscular organ that pumps blood through the body.

Four chambers: Two atria (receive blood) and two ventricles (pump blood).

Valves: Prevent backflow of blood. The heart contracts and relaxes in a rhythmic cycle called the cardiac cycle.

Blood Vessels: Arteries: Carry blood away from the heart. Thick, elastic walls to withstand high pressure.

Veins: Carry blood back to the heart. Thinner walls than arteries, with valves to prevent backflow of blood.

Capillaries: Tiny, thin-walled vessels that connect arteries and veins. Site of exchange of gases, nutrients, and waste products between blood and tissues.