Lesson Notes By Weeks and Term v5 - Grade 11

Lesson Video

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Performance objectives

• Describe the main types of plant tissues and their functions.
• Explain adaptations of xylem and phloem for transport.
• Describe the main types of animal tissues and their functions.
• Differentiate between tissue sub-types (e.g., epithelial, connective).
• Explain how tissues form organs and systems.

Lesson summary

This week, we're revisiting and building upon our understanding of plant and animal tissues. Understanding these tissues is crucial because they are the building blocks of all living organisms. From the food we eat (plants and animals) to our own bodies, tissues determine structure and function. In South Africa, understanding plant tissues is vital for agriculture, a cornerstone of our economy. Knowledge of animal tissues is essential for understanding human health and disease, and for veterinary science. The health of our livestock and indigenous fauna depends on this knowledge.

Lesson notes

Plant Tissues Plant tissues are broadly categorized into meristematic and permanent tissues.

Meristematic Tissues: These are actively dividing cells responsible for plant growth. They are found at the tips of roots and shoots (apical meristems) and in the vascular cambium (lateral meristem).

Apical meristems: Responsible for primary growth (increase in length).

Lateral meristems (Vascular cambium): Responsible for secondary growth (increase in girth).

Permanent Tissues: These tissues are derived from meristematic tissues and have differentiated to perform specific functions.

Parenchyma: The most abundant type of plant tissue. Parenchyma cells are thin-walled, living cells with large vacuoles.

Function: Photosynthesis (in leaves – mesophyll), storage of food and water, secretion, and wound healing.

Example: The fleshy part of an apple is primarily parenchyma tissue. Think of the morogo (African spinach) that many of you grow at home; the leaves are full of parenchyma cells carrying out photosynthesis.

Collenchyma: Provides flexible support to young plant organs. Collenchyma cells have unevenly thickened cell walls.

Function: Provides mechanical support and flexibility.

Example: Found in the petioles (stalks) of leaves and stems of herbaceous plants. This allows them to bend in the wind without breaking.

Sclerenchyma: Provides rigid support to mature plant organs. Sclerenchyma cells have thick, lignified cell walls and are often dead at maturity.

Function: Provides strength and support.

Types: Fibers (long, slender cells) and sclereids (short, irregular cells).

Example: Fibers are found in the stems of flax plants (used to make linen) and sclereids are found in the hard shells of nuts and the gritty texture of pears.

Xylem: A complex tissue responsible for the transport of water and minerals from the roots to the rest of the plant.

Components: Tracheids and vessel elements (both dead at maturity and lignified, providing structural support).

Adaptations: Lignified walls provide strength to withstand negative pressure (tension) during transpiration. Pits (small openings) allow water to move laterally between adjacent xylem cells. Vessels, in particular, allow for highly efficient water transport.

Example: The annual rings in a tree trunk are formed by the xylem tissue produced each year. During the wet season, larger xylem vessels are formed. During the dry season smaller ones are formed, creating the distinct visual rings.

Phloem: A complex tissue responsible for the transport of sugars (produced during photosynthesis) from the leaves to other parts of the plant.

Components: Sieve tube elements (living cells, but lack a nucleus) and companion cells (provide metabolic support to sieve tube elements).

Adaptations: Sieve plates (perforated end walls) allow for the flow of phloem sap between sieve tube elements. Companion cells have numerous mitochondria and ribosomes, providing energy and proteins for sieve tube function.

Example: When you tap a maple tree for sap, you are primarily collecting phloem sap. This sap can then be processed into syrup. This process highlights how phloem distributes sugars throughout the plant. Animal Tissues Animal tissues are broadly categorized into epithelial, connective, muscle, and nervous tissues.

Epithelial Tissue: Covers body surfaces, lines body cavities and organs, and forms glands.

Functions: Protection, secretion, absorption, excretion, filtration, and sensory reception.

Types: Squamous Epithelium: Thin, flat cells. Allows for diffusion and filtration.

Example: Lining of blood vessels (endothelium) and air sacs of the lungs (alveoli).

Cuboidal Epithelium: Cube-shaped cells. Secretion and absorption.

Example: Lining of kidney tubules and glands.

Columnar Epithelium: Column-shaped cells. Secretion and absorption. Often have microvilli (finger-like projections) to increase surface area.

Example: Lining of the small intestine.

Transitional Epithelium: Cells can change shape (from squamous to cuboidal). Allows for stretching.

Example: Lining of the urinary bladder.

Connective Tissue: Supports, connects, and separates different tissues and organs.

Components: Cells (e.g., fibroblasts, chondrocytes, osteocytes), fibers (collagen, elastic, reticular), and ground substance (extracellular matrix).

Types: Connective Tissue Proper: Loose Connective Tissue: Areolar, adipose, and reticular. Fills spaces between organs, cushions and insulates.

Dense Connective Tissue: Regular and irregular. Provides strong attachment between structures. Tendons and ligaments are made of dense regular connective tissue.

Cartilage: Provides support and flexibility. Hyaline, elastic, and fibrocartilage.

Example: Cartilage in the joints, ears, and nose.

Bone: Provides support and protection. Compact and spongy bone.

Blood: Transports oxygen, carbon dioxide, nutrients, and waste products.

Muscle Tissue: Responsible for movement.

Types: Skeletal Muscle: Voluntary movement. Striated (banded) appearance.