Lesson Notes By Weeks and Term v5 - Grade 11

Lesson Video

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Performance objectives

• Describe the structure and function of major plant tissues.
• Describe the structure and function of major animal tissues.
• Explain the relationship between tissue structure and its role.
• Compare adaptations of different tissues to their environment.
• Apply knowledge to real-world South African scenarios.

Lesson summary

In Grade 10, we introduced the fundamental concepts of plant and animal tissues. This week, we'll be revisiting and expanding on that knowledge, delving deeper into the structure and function of various tissues and their significance in the overall physiology of plants and animals. Understanding tissues is crucial because it forms the foundation for understanding how organs function, how diseases affect the body, and how we can develop solutions to improve plant and animal health. For instance, understanding plant vascular tissue helps us develop better irrigation methods for crops in drought-prone regions of South Africa.

Lesson notes

Plant Tissues: Parenchyma: This is the most abundant and versatile plant tissue.

Structure: Thin-walled cells with large vacuoles. Generally spherical or oval in shape.

Function: Photosynthesis (in chlorenchyma, a type of parenchyma containing chloroplasts), storage (of starch, proteins, and oils), secretion, and wound healing. In leaves, parenchyma cells contain chloroplasts and perform photosynthesis. In roots and stems, they can store food. Parenchyma cells are also involved in gas exchange within the plant.

Example: The fleshy part of a fruit is composed mainly of parenchyma cells. Think of the soft flesh of a mango – it's full of parenchyma!

Collenchyma: Provides flexible support, especially in growing regions.

Structure: Elongated cells with unevenly thickened cell walls (due to pectin and cellulose).

Function: Supports young stems, petioles (leaf stalks), and leaf veins, allowing them to bend without breaking. It is found beneath the epidermis.

Example: The strands of celery stalks are made of collenchyma, giving them their characteristic stringy texture and ability to bend.

Sclerenchyma: Provides rigid support and strength.

Structure: Cells with thick, lignified (containing lignin, a complex polymer) cell walls. Often dead at maturity.

Two types: fibers (long and slender) and sclereids (short and irregular).

Function: Provides structural support and protection. Fibers are used commercially to make ropes and textiles. Sclereids contribute to the hardness of seed coats and nut shells.

Example: The gritty texture of a pear is due to sclereids (stone cells). Think of the strong fibers of hemp used to make rope.

Xylem: Transports water and dissolved minerals from the roots to the rest of the plant.

Structure: Composed of tracheids and vessel elements (both dead at maturity), which are elongated cells with thick, lignified walls. Tracheids are narrower and have pits (small openings) for water to pass through. Vessel elements are wider and have perforations (large openings) at the ends.

Function: Water transport and structural support.

Example: The "wood" of a tree is primarily composed of xylem.

Phloem: Transports sugars (produced during photosynthesis) from the leaves to other parts of the plant.

Structure: Composed of sieve tube elements (living cells, but lacking a nucleus and ribosomes at maturity) and companion cells (which support the sieve tube elements). Sieve tube elements are connected by sieve plates (perforated end walls) that allow the flow of sugars.

Function: Sugar transport.

Example: Phloem is responsible for transporting the sugars produced in the leaves of a sugarcane plant to the stem, where they are stored.

Epidermis: The outer protective layer of the plant.

Structure: A single layer of tightly packed cells, often covered with a waxy cuticle to prevent water loss. May contain specialized cells such as guard cells (which regulate the opening and closing of stomata for gas exchange) and trichomes (hair-like structures that can protect against herbivores or reduce water loss).

Function: Protection from water loss, pathogens, and herbivores. Gas exchange through stomata.

Example: The shiny surface of a leaf is due to the cuticle secreted by epidermal cells.