Lesson Notes By Weeks and Term v5 - Grade 10

Lesson Video

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Performance objectives

• Define 'tissue' and its role.
• Describe main plant tissues: parenchyma, collenchyma, sclerenchyma, xylem, and phloem.
• Describe main animal tissues: epithelial, connective, muscle, and nervous.
• Compare and contrast plant and animal tissues.
• Relate tissue structure to its function.

Lesson summary

This week, we delve into the fascinating world of plant and animal tissues. Tissues are groups of similar cells performing specific functions within an organism. Understanding tissues is fundamental to understanding how living organisms function. In South Africa, where agriculture and animal husbandry are crucial to our economy and food security, knowledge of plant and animal tissues is essential. For example, understanding how plant vascular tissues transport water and nutrients can help farmers optimize irrigation and fertilization techniques. Similarly, understanding animal muscle tissue is important for meat production and animal health management.

Lesson notes

What are Tissues? A tissue is a group of similar cells that perform a specific function. These cells work together to carry out complex tasks that contribute to the overall survival and functioning of the organism. Multicellular organisms rely on tissues for organization, specialisation and efficiency. Without tissues, organisms would be a mass of undifferentiated cells unable to carry out complex life processes. Plant Tissues Plants have various tissue types, each with a specific function: Parenchyma: This is the most common type of plant tissue. Parenchyma cells are generally thin-walled and relatively undifferentiated. They are involved in various functions, including photosynthesis, storage of food and water, and wound healing.

Example: the fleshy part of a fruit like a mango is primarily composed of parenchyma cells storing sugars and water. In a leafy vegetable such as spinach, the mesophyll (the middle layer of leaf tissue) is made of parenchyma cells containing chloroplasts for photosynthesis.

Structure:* Thin cell walls, large vacuoles.

Function:* Photosynthesis, storage, secretion, wound repair.

Collenchyma: Collenchyma tissue provides flexible support to young stems and leaves. Collenchyma cells have unevenly thickened cell walls, allowing them to withstand bending and stretching without breaking.

Example: The stalks of celery are supported by collenchyma.

Structure:* Unevenly thickened cell walls.

Function:* Flexible support.

Sclerenchyma: Sclerenchyma tissue provides rigid support and protection to plant parts. Sclerenchyma cells have thick, lignified cell walls, making them very strong and durable.

There are two types: sclereids (stone cells) and fibres.

Example: Sclerenchyma is found in the shells of nuts and the gritty texture of pears is due to sclereids. Fibres are found in flax, hemp and jute which are used to make ropes and fabrics.

Structure:* Thick, lignified cell walls.

Function:* Rigid support, protection.

Xylem: Xylem tissue is responsible for transporting water and minerals from the roots to the rest of the plant. Xylem cells are dead at maturity and form long, continuous tubes. Tracheids and vessel elements are the main types of xylem cells.

Example: Think of the large trees in Kruger National Park - their massive size is only possible because of the efficient water transport provided by xylem.

Structure:* Dead cells with thick walls, forming tubes.

Function:* Water and mineral transport.

Phloem: Phloem tissue is responsible for transporting sugars produced during photosynthesis from the leaves to other parts of the plant. Phloem cells are living but lack a nucleus and other organelles. Sieve tube elements and companion cells are the main types of phloem cells.

Example: In sugarcane farming regions of KwaZulu-Natal, phloem efficiently transports sucrose from the leaves to the stem, where it's stored.

Structure:* Living cells with sieve plates, companion cells.

Function:* Sugar transport. Animal Tissues Animals also have diverse tissue types, each with specialized roles: Epithelial Tissue: Epithelial tissue covers surfaces of the body, both inside and out. It forms a protective barrier and can also be involved in secretion and absorption.

Example: The skin is an epithelial tissue protecting the body from the outside environment. The lining of the small intestine is also an epithelial tissue absorbing nutrients from digested food.

Structure:* Tightly packed cells, forming sheets. Can be squamous, cuboidal, or columnar.

Function:* Protection, secretion, absorption, excretion.

Connective Tissue: Connective tissue supports and connects other tissues in the body. It includes a variety of cell types and a matrix of extracellular material.

Example: Bone and cartilage support the body and protect organs. Blood transports oxygen, nutrients, and waste products. Adipose tissue (fat) stores energy and provides insulation.

Structure:* Cells scattered in a matrix.

Function:* Support, connection, transport, storage, insulation.

Types:* Blood, bone, cartilage, adipose tissue.

Muscle Tissue: Muscle tissue is responsible for movement.

There are three types: skeletal muscle (voluntary movement), smooth muscle (involuntary movement), and cardiac muscle (heartbeat).

Example: Skeletal muscle allows us to walk, run, and lift objects. Smooth muscle controls the movement of food through the digestive system. Cardiac muscle pumps blood throughout the body.

Structure:* Elongated cells, containing contractile proteins.

Function:* Movement.

Types:* Skeletal, smooth, cardiac.

Nervous Tissue: Nervous tissue is responsible for transmitting electrical signals throughout the body. It consists of neurons (nerve cells) and glial cells (supporting cells).

Example: The brain and spinal cord are made of nervous tissue. Neurons transmit information from the sensory organs to the brain and from the brain to the muscles and glands.

Structure:* Neurons with long extensions (axons and dendrites).