FPSC (Federal Public Service Commission) · CSS (Central Superior Services)
Plant Structure & Growth
7. Plants & Animals
· General Science/Everyday Science
124 MCQs
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1–20
of 124 MCQs
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1
Which plant tissue is responsible for the primary growth (lengthening) of stems and roots?
Answer:
Apical meristem
Apical meristems are located at the tips of roots and shoots. They contain undifferentiated cells that divide rapidly, leading to the extension of the plant body, a process known as primary growth.
2
Which of the following cell types is dead at functional maturity and facilitates water transport?
Answer:
Tracheids
Tracheids and vessel elements are the two types of water-conducting cells in the xylem. Both are dead at maturity, leaving behind thickened cell walls that form a hollow tube for efficient water and mineral transport.
3
The 'Casparian strip' is a waterproof barrier found in which layer of the root?
Answer:
Endodermis
The endodermis is the innermost layer of the root cortex. The Casparian strip is a belt made of suberin that forces water and minerals to cross the plasma membrane of endodermal cells, acting as a selective checkpoint.
4
Which plant hormone is primarily responsible for 'apical dominance'?
Answer:
Auxin
Auxin produced in the terminal bud inhibits the growth of axillary buds. This phenomenon ensures that the plant grows taller toward light rather than branching out excessively from the sides.
5
In a leaf, most photosynthesis occurs in which specific tissue layer?
Answer:
Palisade mesophyll
The palisade mesophyll consists of column-shaped cells located just beneath the upper epidermis. They are packed with chloroplasts and arranged vertically to maximize light absorption for photosynthesis.
6
What is the primary function of guard cells in the epidermis of a leaf?
Answer:
Regulate the opening and closing of stomata
Guard cells change shape based on their turgor pressure. When they take up water, they bow outward to open the stoma, allowing for gas exchange (CO2 in, O2 out), and they close to prevent excessive water loss during transpiration.
7
Which tissue produces secondary xylem and secondary phloem during secondary growth?
Answer:
Vascular cambium
The vascular cambium is a cylinder of meristematic cells. It divides to produce secondary xylem (wood) toward the interior of the stem and secondary phloem toward the exterior, increasing the plant's girth.
8
Which of the following is characteristic of monocot stems compared to dicot stems?
Answer:
Vascular bundles scattered throughout the ground tissue
In monocots like corn or grass, the vascular bundles are distributed throughout the ground tissue. In eudicots (dicots), the vascular bundles are typically arranged in a ring, allowing for more organized secondary growth.
9
Root hairs are extensions of which cell type?
Answer:
Epidermal cells
Root hairs are tiny, finger-like projections of epidermal cells near the root tip. They significantly increase the surface area available for the absorption of water and dissolved minerals from the soil.
10
Which plant hormone is a gas and is involved in fruit ripening?
Answer:
Ethylene
Ethylene is unique among plant hormones because it is a gas. It triggers a cascade of chemical reactions that lead to the breakdown of starches into sugars and the softening of cell walls during fruit ripening.
11
The lateral roots of a plant originate from which tissue layer?
Answer:
Pericycle
Lateral roots arise from the pericycle, which is the outermost layer of the vascular cylinder (stele). This allows the new root to maintain connection with the xylem and phloem of the main root.
12
Which type of plant cell provides flexible support to young parts of the plant shoot?
Answer:
Collenchyma
Collenchyma cells have unevenly thickened primary cell walls. They provide structural support without restricting growth, which is why they are found in growing stems and petioles.
13
Which plant hormone is responsible for stem elongation and the 'bolting' of plants?
Answer:
Gibberellins
Gibberellins promote cell elongation and division in stems. Bolting is the rapid growth of a floral stalk from a rosette-style plant, triggered by environmental cues and gibberellin production.
14
What happens to the water potential of guard cells when they pump in potassium (K+) ions?
Answer:
Water potential decreases
As K+ ions enter the guard cells, the solute concentration increases, which lowers the water potential. This causes water to flow into the cells via osmosis, making them turgid and opening the stomata.
15
Which of the following describes 'determinate' growth?
Answer:
Growth that stops after an organ reaches a certain size
Determinate growth is seen in organs like leaves and flowers, which reach a final size and stop growing. Indeterminate growth is seen in stems and roots, which can grow for as long as the plant lives.
16
Which cells in the phloem are alive but lack a nucleus, ribosomes, and a distinct vacuole?
Answer:
Sieve-tube elements
Sieve-tube elements are specialized for sugar transport. They lose most organelles to reduce resistance to flow, relying on neighboring companion cells for metabolic support.
17
What are 'lenticels' in the bark of a woody plant?
Answer:
Pores that allow for gas exchange
Lenticels are raised, porous areas in the periderm (bark) of woody stems and roots. They enable the internal living tissues to exchange oxygen and carbon dioxide with the atmosphere.
18
Which hormone promotes seed dormancy and inhibits growth during drought conditions?
Answer:
Abscisic acid (ABA)
ABA acts as a stress hormone. It signals the stomata to close during water shortages and maintains seed dormancy so that germination only occurs under favorable conditions.
19
Which specialized roots provide extra support to tall, heavy-topped plants like corn?
Answer:
Prop roots
Prop roots are adventitious roots that grow from the stem above the ground. They extend into the soil to provide additional stability for top-heavy plants.
20
The 'heartwood' of an old tree consists of:
Answer:
Older, non-functional secondary xylem
As a tree ages, the oldest layers of secondary xylem stop conducting water and become filled with resins and tannins. This heartwood provides structural support, while the outer sapwood conducts water.
