Unit 5 Diversity of specialised tissues
Key unit competence: Examine different specialised plant and animal cells, and adaptation of tissues.
Key ideas
- A tissue is a group of similar cells (with intercellular material) working together to perform a function. Tissues form organs, organs form organ systems, and systems form the organism.
- Meristematic tissues in plants are made of small, thin-walled, actively dividing cells with dense cytoplasm and no large vacuoles: apical meristems (root and shoot tips: growth in length, primary growth), lateral meristems (vascular cambium and cork cambium: growth in thickness, secondary growth) and intercalary meristems (at nodes of grasses).
- Permanent tissues: parenchyma (thin-walled living cells; storage, photosynthesis as chlorenchyma, packing), collenchyma (living cells with walls thickened at the corners; flexible support in young stems and leaf stalks), sclerenchyma (dead cells with thick lignified walls: fibres and sclereids; strength), and epidermis (protection, cuticle, stomata, root hairs).
- Vascular tissues: xylem (vessels, tracheids, xylem fibres and parenchyma; transports water and minerals and gives support) and phloem (sieve tubes, companion cells, phloem parenchyma and fibres; transports organic solutes).
- Animal tissues: epithelial, muscular, nervous and connective tissue.
- Epithelium covers surfaces and lines cavities; cells sit on a basement membrane. Squamous (flat; alveoli, blood capillaries: diffusion), cuboidal (kidney tubules, glands: secretion and absorption), columnar (intestine: absorption, often with microvilli), ciliated (trachea, oviduct: moves mucus or ova), stratified (many layers; skin, oesophagus: protection).
- Muscle tissue: skeletal (striated, voluntary): long multinucleate fibres attached to bones; smooth (unstriated, involuntary): spindle-shaped cells with one nucleus in gut and blood vessel walls; cardiac: striated, branched, with intercalated discs, contracts rhythmically without tiring (myogenic).
- Nervous tissue: neurones (cell body, dendrites, axon) carry impulses; glial cells support them. Connective tissue has cells in a matrix: blood (plasma matrix), bone (calcium phosphate matrix, osteocytes), cartilage (chondrocytes in a firm matrix), adipose (fat storage, insulation), tendons and ligaments (collagen and elastic fibres).
- Unicellular organisms: one cell carries out all life processes; large surface area to volume ratio, so diffusion is enough; fast reproduction; but limited size and no division of labour. Multicellular organisms: division of labour and specialisation, larger size, longer life, but need transport and coordination systems and more energy to grow.
Common misconceptions
- "All plant tissues are living." No: xylem vessels and sclerenchyma fibres are dead at maturity.
- "Cardiac muscle is the same as skeletal muscle." No: cardiac muscle is branched, has intercalated discs, is involuntary and does not tire.
- "Blood is not a tissue because it is liquid." No: blood is a connective tissue: cells in a liquid matrix (plasma).
- "Meristem cells have large vacuoles." No: they have small vacuoles and dense cytoplasm because they divide actively.
Worked examples
Example 1. Explain how squamous epithelium in the alveoli and columnar epithelium in the ileum are each adapted to their function.
Solution
Squamous cells are very thin and flat, giving a short diffusion distance for O₂ and CO₂ in the alveoli. Columnar cells are tall with microvilli (large surface area) and many mitochondria for active absorption of digested food in the ileum; some secrete mucus.
Example 2. Compare the three types of muscle tissue.
Solution
Skeletal: striated, long multinucleate fibres, voluntary, tires quickly, moves bones. Smooth: unstriated, spindle-shaped, one nucleus, involuntary, slow and sustained (gut, blood vessels). Cardiac: striated, branched cells with one nucleus and intercalated discs, involuntary, contracts rhythmically without fatigue (heart).
Practice questions
Define tissue and name the four main animal tissues.
Show answer
A tissue is a group of similar cells working together to perform a function. Epithelial, muscular, nervous and connective.
Common mistake: Calling organs tissues.
Distinguish between apical and lateral meristems.
Show answer
Apical meristems at root and shoot tips cause growth in length (primary growth); lateral meristems (vascular and cork cambium) cause growth in thickness (secondary growth).
Common mistake: Saying apical meristems increase girth.
Compare parenchyma, collenchyma and sclerenchyma.
Show answer
Parenchyma: living, thin walls, storage/photosynthesis/packing. Collenchyma: living, walls thickened at corners, flexible support. Sclerenchyma: dead, thick lignified walls, mechanical strength.
Common mistake: Saying collenchyma is dead.
Name four types of epithelium and give one location of each.
Show answer
Squamous (alveoli, capillaries); cuboidal (kidney tubules, glands); columnar (stomach, intestine); ciliated (trachea, oviduct); stratified (skin, oesophagus).
Common mistake: Giving locations of muscle.
Give three differences between skeletal and smooth muscle.
Show answer
Skeletal: striated, multinucleate long fibres, voluntary, fast contraction, tires quickly. Smooth: unstriated, spindle cells with one nucleus, involuntary, slow sustained contraction.
Common mistake: Saying smooth muscle is voluntary.
State three types of connective tissue and their functions.
Show answer
Bone: support and protection; cartilage: smooth joints and flexible support; blood: transport; adipose: energy store and insulation; tendons/ligaments: attach muscle to bone/bone to bone.
Common mistake: Including epithelium.
State two advantages and two disadvantages of being multicellular.
Show answer
Advantages: specialisation/division of labour; larger size; longer life; better survival in varied environments. Disadvantages: need transport and coordination systems; slower reproduction; more energy needed.
Common mistake: Listing only advantages.
Explain the levels of organisation with an example.
Show answer
Cell (muscle cell) → tissue (cardiac muscle) → organ (heart) → organ system (circulatory system) → organism (human).
Common mistake: Putting organ before tissue.
Matching and drag-and-drop
Matching
Match each item in column A with the correct answer in column B. Write the letter next to each number.
Column A Column B 1. Actively dividing plant tissue is: a. collagen fibres 2. Tendons and ligaments contain mainly: b. parenchyma 3. Fat-storing connective tissue is: c. meristem 4. Thin-walled living cells used for storage are: d. adipose tissue Show answer
1 → c (meristem) · 2 → a (collagen fibres) · 3 → d (adipose tissue) · 4 → b (parenchyma)
- Found at root and shoot tips.
- Collagen gives tensile strength.
- It insulates and stores energy.
- Potato tubers are mainly parenchyma.
Drag and drop
Choose the correct word or phrase from the box for each gap. One word in the box is not needed.
collenchyma · smooth muscle · tissue · organism- Cells with walls thickened at the corners giving flexible support are .
- A group of similar cells working together forms a .
- Muscle in the walls of the gut is .
Show answer
1: collenchyma · 2: tissue · 3: smooth muscle
- Found in young stems and petioles.
- Example: xylem.
- It causes peristalsis.
Matching
Match each item in column A with the correct answer in column B. Write the letter next to each number.
Column A Column B 1. The trachea is lined by: a. chlorenchyma 2. Growth in thickness of stems is caused by: b. a large surface area to volume ratio 3. Parenchyma with chloroplasts is called: c. ciliated epithelium 4. A feature of unicellular organisms is: d. lateral meristems (cambium) Show answer
1 → c (ciliated epithelium) · 2 → d (lateral meristems (cambium)) · 3 → a (chlorenchyma) · 4 → b (a large surface area to volume ratio)
- Cilia move mucus.
- This is secondary growth.
- It carries out photosynthesis.
- Diffusion is enough.
Drag and drop
Choose the correct word or phrase from the box for each gap. One word in the box is not needed.
stratified epithelium · collenchyma · cardiac muscle · cuboidal epithelium- A young bean stem bends without breaking. This flexibility is mainly due to .
- Kidney tubules are lined by .
- The skin is protected by .
Show answer
1: collenchyma · 2: cuboidal epithelium · 3: stratified epithelium
- Its living cells have thickened corners.
- Cells absorb and secrete.
- Many layers resist wear.