Tissues: Plant and Animal Tissues
ICSE Class 9 · Biology · Chapter 3
What this chapter covers
- What a tissue is
- Plant tissues: meristematic tissue
- Plant tissues: simple permanent tissues
- Plant tissues: complex permanent tissues
- Animal tissues: epithelial tissue
- Animal tissues: connective tissue
- Animal tissues: muscular tissue
- Animal tissues: nervous tissue
- Role of tissues in physiological processes in plants
- Role of tissues in physiological processes in animals
Key points
- A tissue is a group of cells similar in origin, structure and function working together; tissues make organs, organs make organ systems.
- Plant tissues are meristematic (dividing) or permanent (non-dividing).
- Apical meristem gives growth in length, intercalary meristem lengthens internodes and regrows grass, and lateral meristem increases girth.
- Simple permanent tissues: parenchyma (living, thin-walled; storage and food-making), collenchyma (living, corner-thickened; flexible support) and sclerenchyma (dead, lignified fibres and sclereids; strength).
- Epidermis with cuticle and stomata, and cork with suberin, are protective tissues.
- Xylem (tracheids, vessels, xylem parenchyma, xylem fibres) carries water and minerals upward and gives support.
- Phloem (sieve tubes, companion cells, phloem parenchyma, phloem fibres) carries food both ways by translocation.
- The four basic animal tissues are epithelial, connective, muscular and nervous.
- Epithelium covers and lines: squamous, stratified squamous, cuboidal, columnar, ciliated and glandular.
- Connective tissue has scattered cells in a large matrix: areolar, adipose, tendon, ligament, cartilage, bone, blood and lymph.
- Muscle is striated (voluntary, limbs), unstriated (involuntary, gut walls) or cardiac (involuntary, heart, never tires).
- Nervous tissue is made of neurons (cell body, dendrites, axon) and carries electrical impulses.
- Every physiological process, such as photosynthesis, transport, digestion, breathing or movement, depends on several tissues working together.
Questions answered
Define a tissue and explain what is meant by division of labour.
A tissue is a group of cells similar in origin, structure and function that work together to perform a particular function. Division of labour is the sharing of different life activities among different groups of specialised cells, so that each group does one job efficiently.
Give two features of meristematic cells that suit them for division.
Any two: a thin cellulose wall; dense cytoplasm with a large nucleus; no or very small vacuoles; closely packed cells with no intercellular spaces.
Why does a lawn grow again after it is mown?
Grasses have intercalary meristem at the base of their leaves and internodes. Mowing removes the upper parts but leaves this meristem, which divides and regrows the grass.
Name the meristem responsible for (a) growth in length of a root, (b) increase in girth of a tree trunk.
(a) Apical meristem. (b) Lateral meristem (vascular cambium and cork cambium).
State two differences between collenchyma and sclerenchyma.
Collenchyma cells are living, while sclerenchyma cells are dead. Collenchyma walls are thickened at the corners with cellulose and pectin, while sclerenchyma walls are uniformly thickened with lignin.
What is aerenchyma? Where is it found?
Aerenchyma is parenchyma with large air spaces between its cells. It is found in aquatic plants such as the lotus and water hyacinth, where it gives buoyancy and supplies air to submerged parts.
Name the elements of xylem. Which of them is living?
Tracheids, vessels, xylem parenchyma and xylem fibres. Only xylem parenchyma is living.
Give two differences between xylem and phloem.
Xylem conducts water and minerals, while phloem conducts prepared food. Xylem conducts only upward, while phloem conducts both upward and downward. (Also: xylem is mostly dead, phloem mostly living.)