Tissues — Practice

Question 1

Define a tissue.

Accepted Answer

Step 1 — State the definition.
  A tissue is a group of similar cells, along with intercellular substances, that perform a specific function in the body.

Step 2 — Key elements of the definition.
  • Similar cells (not random cells).
  • Intercellular substances (matrix).
  • A specific function (not just being grouped).

✦ Answer: A tissue is a group of similar cells together with intercellular substances that perform a specific function.

Question 2

Name the meristem responsible for growth in girth of a plant.

Accepted Answer

Step 1 — Recall three meristem types.
  Apical → length. Lateral → girth. Intercalary → regrowth.

✦ Answer: Lateral meristem (also called cambium) — responsible for secondary growth = increase in girth.

Question 3

Identify the tissue: lines the alveoli of the lungs, single layer of flat scale-like cells.

Accepted Answer

Step 1 — Locate where described.
  Lining of alveoli + single layer + flat cells = SIMPLE SQUAMOUS EPITHELIUM.

✦ Answer: Simple squamous epithelium.

The thinness (just one cell layer of flat cells) is perfect for rapid gas exchange.

Question 4

Which animal tissue has a fluid matrix?

Accepted Answer

Step 1 — Recall: most connective tissues have a matrix.
  Blood has a FLUID matrix called plasma — unique among tissues.

Step 2 — Other matrices.
  Bone: hard calcified matrix. Cartilage: gel-like. Areolar: jelly-like.

✦ Answer: Blood. Its plasma matrix is unique in being fluid.

Question 5

State two functions each of xylem and phloem.

Accepted Answer

Step 1 — Xylem.
  (i) Transports water and minerals from roots to leaves (one-way, upward).
  (ii) Provides mechanical support to the plant (lignified secondary walls form wood).

Step 2 — Phloem.
  (i) Transports food (sucrose, amino acids) from leaves to other parts (bidirectional — translocation).
  (ii) Stores food in phloem parenchyma during off-season.

✦ Answer: Xylem — water/mineral transport upward; mechanical support. Phloem — food (sucrose) transport in both directions; storage.

Question 6

Identify the plant tissue: dead cells, very thick walls, makes the husk of coconut. State two of its functions.

Accepted Answer

Step 1 — Identify the tissue.
  Dead cells + very thick walls + protective in coconut husk = SCLERENCHYMA.

Step 2 — Functions.
  (i) Mechanical support — its lignified walls give the plant rigidity.
  (ii) Protection — the hard tissue of the coconut husk protects the seed from physical damage.
  Also: water-impermeability, resistance to mechanical stress.

✦ Answer: Sclerenchyma. Functions — mechanical support and protection.

Question 7

State three differences between striated and smooth muscle fibres.

Accepted Answer

Step 1 — Lay out a comparison.

| Feature | Striated (skeletal) | Smooth |
  |---------|---------------------|---------|
  | Striations | Present (cross-bands visible under microscope) | Absent |
  | Shape | Long, cylindrical | Spindle-shaped (pointed at ends) |
  | Nuclei | Multinucleated | Single nucleus, central |
  | Control | Voluntary (consciously controlled) | Involuntary |
  | Location | Attached to bones | Walls of gut, blood vessels, iris |

✦ Answer: Striated: cross-banded, multinucleated, voluntary, in skeletal muscle. Smooth: no striations, single nucleus, involuntary, in internal organs and blood vessels.

Question 8

Identify the tissue type based on these descriptions: (a) Connects bone to bone, very strong and slightly stretchable. (b) Forms the inner lining of the small intestine, has cilia/brush border to absorb nutrients. (c) Located between vertebrae, acts as shock absorber.

Accepted Answer

Step 1 — Identify each.

(a) Connects bone to bone + strong + slightly stretchable → LIGAMENT (fibrous connective tissue).

(b) Inner lining of small intestine + brush border for absorption → COLUMNAR EPITHELIUM (specifically simple columnar with microvilli).

(c) Between vertebrae + shock absorber → CARTILAGE (specifically intervertebral discs are made of fibrocartilage).

✦ Answer: (a) Ligament, (b) Columnar epithelium, (c) Cartilage.

Question 9

Why is xylem mostly dead but still functional?

Accepted Answer

Step 1 — Recall xylem's main job.
  Transport water + minerals from roots to leaves in continuous columns.

Step 2 — How being dead helps.
  • Living cells contain cytoplasm and organelles — these would impede the upward flow of water.
  • Dead xylem vessels and tracheids are HOLLOW tubes — water flows through them freely.
  • Their thick, lignified walls prevent collapse under the high tension of transpiration pull.

Step 3 — But not entirely dead.
  Xylem parenchyma (one of the 4 xylem cell types) is LIVING and stores food.

✦ Answer: The transport function needs HOLLOW tubes with strong walls. Dead, hollow tracheids and vessels are functionally ideal — they offer no internal obstruction to water flow, while their lignified walls resist the negative pressure of transpiration. (Xylem parenchyma is living and handles food storage.)

Question 10

Why are stomata important for a plant? Describe their structure and one of their functions.

Accepted Answer

Step 1 — Structure.
  Stomata are tiny pores in the epidermis (mainly on lower leaf surface), each flanked by a pair of bean-shaped GUARD CELLS.
  Guard cells contain chloroplasts and have UNEVENLY THICKENED walls — thin on the outside, thick on the inside.
  When turgid (water-filled), guard cells bend outward, opening the pore. When flaccid, they collapse inward, closing it.

Step 2 — Functions (any one for 1 mark, but here's two):
  (i) GAS EXCHANGE — CO₂ enters for photosynthesis; O₂ exits.
  (ii) TRANSPIRATION — water vapour exits, creating the suction that pulls water up the xylem.
  (iii) Cooling — evaporative cooling of the leaf surface (similar to sweating).

✦ Answer: Stomata are pores on the leaf epidermis, flanked by guard cells. They control gas exchange (CO₂ in, O₂ out) for photosynthesis and allow transpiration. Their opening/closing is regulated by turgor pressure in the guard cells.

Question 11

Compare cardiac and skeletal muscles on four features. Then explain why cardiac muscle never fatigues but skeletal muscle does.

Accepted Answer

Step 1 — Compare on four features.

| Feature | Skeletal | Cardiac |
  |---------|----------|---------|
  | Control | Voluntary | Involuntary |
  | Branching | Unbranched | Branched |
  | Nuclei | Multinucleated | Single nucleus, central |
  | Striations | Yes | Yes |
  | Joins between cells | None | Intercalated discs |
  | Location | Throughout body, attached to bones | Heart wall only |

Step 2 — Why cardiac doesn't fatigue.
  Cardiac muscle cells have an EXTREMELY HIGH density of mitochondria → continuous ATP production from aerobic respiration.
  They use FATTY ACIDS in addition to glucose, providing more energy per gram.
  Intercalated discs allow rapid synchronised contraction, so each cell rests briefly between beats.
  Skeletal muscle, in contrast, often relies on anaerobic glycolysis (especially under heavy load), which accumulates LACTIC ACID — and that's what gives the burning fatigue feeling.

✦ Answer: Comparison above. Cardiac doesn't fatigue because (i) high mitochondria → aerobic respiration; (ii) uses fatty acids efficiently; (iii) rhythmic synchronisation gives each cell brief recovery between beats. Skeletal fatigues due to anaerobic respiration → lactic acid buildup.

Question 12

(a) Draw a labelled diagram of a neuron showing the cell body, dendrites, axon and synapse. (b) Briefly explain how a signal travels along it.

Accepted Answer

Step 1 (a) — Neuron diagram (described in words; you should draw it for the exam):

Dendrites (multiple short branches at one end)
         |
  Cell body (contains nucleus, lots of cytoplasm)
         |
  Axon (long single process; can be > 1 m in length)
         |
  Axon terminals (branches at the far end)
         |
  Synapse (gap between axon terminal of this neuron and dendrite of the next)

Step 2 (b) — Signal flow.
  1. DENDRITES receive electrical/chemical signals from adjacent neurons or sensory receptors.
  2. If the combined signal is strong enough, an ACTION POTENTIAL (electrical impulse) is triggered at the CELL BODY.
  3. The impulse travels along the AXON to the axon terminals.
  4. At the SYNAPSE, the impulse triggers release of NEUROTRANSMITTERS (chemical messengers) across the synaptic gap.
  5. Neurotransmitters bind to receptors on the next neuron's dendrites, initiating a new signal.

✦ Answer: Diagram with 4 labels (dendrites, cell body, axon, synapse). Signal: dendrites receive → cell body integrates → axon carries action potential → axon terminal releases neurotransmitter → next neuron's dendrite receives.

Question 13

Differentiate aerenchyma, chlorenchyma and storage parenchyma. Give one example plant for each.

Accepted Answer

Step 1 — All three are types of parenchyma. They differ in structure and function.

• Aerenchyma:
    Has large AIR SPACES between cells.
    Function: buoyancy (helps the plant float).
    Example: water hyacinth (Eichhornia), lotus.

• Chlorenchyma:
    Contains CHLOROPLASTS.
    Function: photosynthesis.
    Example: green leaves (mesophyll tissue), green stems of cactus.

• Storage parenchyma:
    Stores STARCH, oils, water.
    Function: nutrient reserve.
    Example: potato tuber, carrot root, succulent stems of cactus.

✦ Answer: All are parenchyma variants. Aerenchyma → big air spaces for buoyancy (water hyacinth). Chlorenchyma → has chloroplasts for photosynthesis (leaves). Storage parenchyma → stores food (potato).

Question 14

Compare epithelial tissue and connective tissue on at least 4 features.

Accepted Answer

Step 1 — Lay out a clean comparison.

| Feature | Epithelial | Connective |
  |---------|------------|------------|
  | Cell density | Tightly packed | Loosely arranged (cells embedded in matrix) |
  | Intercellular substance | Minimal or none | Abundant matrix (fluid, jelly, solid, or fibrous) |
  | Location | Surfaces & linings (skin, gut, vessels) | Beneath surfaces; supports/connects other tissues |
  | Function | Protection, absorption, secretion | Support, binding, transport (blood), storage |
  | Examples | Squamous, columnar, cuboidal | Areolar, adipose, blood, bone, cartilage |

Step 2 — Key takeaway.
  Epithelium = surface/border tissue (think wallpaper). Connective tissue = support/filler (think wall framing and stuffing).

✦ Answer: Five comparable features above. Most important: cells packed (epithelial) vs cells in matrix (connective); on the surface (epithelial) vs underneath/within (connective).

Question 15

You're given microscopic slides of: (a) a section of the heart wall, (b) blood, (c) a piece of leaf, (d) the lining of small intestine. Identify the tissue type and ONE distinctive structural feature for each.

Accepted Answer

Step 1 — Identify each.

(a) Heart wall: CARDIAC MUSCLE.
   Distinctive feature: branched striated cells with intercalated discs between cells.

(b) Blood: CONNECTIVE TISSUE (specifically blood).
   Distinctive feature: fluid matrix (plasma) with floating red blood cells (biconcave, no nucleus in mature mammalian RBCs), white blood cells (large, nucleated) and platelets.

(c) Leaf: PLANT TISSUES — predominantly CHLORENCHYMA (a type of parenchyma) in the mesophyll.
   Distinctive feature: green colour due to chloroplasts; thin cell walls; intercellular air spaces.
   The leaf also shows xylem and phloem in veins, plus epidermis with stomata on the lower surface.

(d) Lining of small intestine: COLUMNAR EPITHELIUM.
   Distinctive feature: tall pillar-like cells with microvilli at the apical surface (brush border for absorption).

✦ Answer: (a) Cardiac muscle — branched striated cells, intercalated discs. (b) Blood — fluid matrix + RBCs/WBCs. (c) Chlorenchyma — chloroplasts, air spaces (with veins of xylem/phloem). (d) Columnar epithelium — tall cells with microvilli.

Practice — Tissues

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