Plant Tissues and Reproduction – NDA Biology Notes

1. Introduction

Plants are built from an organised hierarchy of cells, tissues, and organs. Unlike animals, plants grow continuously throughout their lives, adding new cells at specific growth zones called meristems. They also reproduce sexually through flowers, producing seeds and fruits.

This chapter covers two connected themes: how plant tissues are classified and what each tissue does; and how flowering plants reproduce, from flower structure to pollination, fertilisation, seed formation, and fruit development.

Plant tissues: Distinguish meristematic from permanent tissue, living from dead cells, xylem from phloem. Plant reproduction: Correct sequence of events, ploidy in double fertilisation, which structures become seeds vs fruits.

2. Plant Tissue Classification Overview

Plant tissues are broadly divided into two major categories: Meristematic tissues (actively dividing cells responsible for growth) and Permanent tissues (cells that have stopped dividing and differentiated into specific structures).

Permanent tissues are further divided into:

• Simple permanent tissues: made of one cell type: parenchyma, collenchyma, sclerenchyma.

• Complex permanent tissues: made of more than one cell type: xylem, phloem.

3. Meristematic Tissues

Growth in plants occurs due to the division of cells of meristematic tissues.  [NDA 2018-I]

Key properties of meristematic cells:

• Small, compactly arranged cells with no intercellular spaces

• Large nucleus relative to cell size

• Thin cell walls: actively dividing

• Living cells: NOT dead.  [NDA 2018-I]

Three Types of Meristematic Tissue

Meristem Type	Location	Function
Apical meristem	Root tips and shoot tips	Increases length of roots and shoots (primary growth)
Lateral meristem (Cambium)	Along sides of stem and root	Increases girth (secondary growth)  [NDA 2021-II | NDA 2025-I]
Intercalary meristem	Base of leaves or internodes	Regrowth after grazing; typical in grasses

Apical Meristem and Length

Damage to the apical meristem of a growing young plant will affect the length of the plant: apical meristems are responsible for primary elongation growth.  [NDA 2018-II] It does NOT affect flower colour, leaf colour, or fruit taste.

Lateral Meristem and Girth

Girth of the stem increases due to the division of cells in the lateral meristem only.  [NDA 2021-II] Cambium is the classic example of a lateral meristem.  [NDA 2025-I]

Cambium sits between xylem and phloem. It divides to produce new xylem inward (wood) and new phloem outward. Apical and intercalary meristems do NOT contribute to girth increase.

Cell Differentiation

The process by which meristematic cells transform into specific permanent tissue cells is called cell differentiation.  [NDA 2021-I] Not cell division, not cell multiplication, not cell regeneration.

4. Simple Permanent Tissues

Parenchyma: The Basic Packing Tissue

Parenchyma is the basic packing tissue of plants.  [NDA 2021-II]

• Living cells
• Thin, cellulose cell walls
• Has intercellular spaces (gaps between cells)
• Found throughout the plant: cortex, pith, mesophyll
• Found in both xylem and phloem as the packing component.  [NDA 2021-II]

Parenchyma does NOT lack intercellular spaces, it definitely has them.  [NDA 2019-II]

Chlorenchyma: Parenchyma with Chloroplasts

Chlorenchyma is a specialised form of parenchyma that contains chloroplasts.  [NDA 2013-I]

• Formed by the palisade and spongy mesophyll
• A form of parenchyma containing chloroplasts
• Carries out photosynthesis: does NOT transport organic solutes (that is phloem)
• NOT a thin transparent protective layer (that describes epidermis)

Aerenchyma: Parenchyma with Air Sacs

Aerenchyma is parenchyma with large air-filled cavities providing buoyancy to aquatic plants. The air sacs in aquatic plants are surrounded by parenchyma tissue.  [NDA 2022-I] Not collenchyma, not sclerenchyma, not complex tissue.

Collenchyma: Flexible Support

Collenchyma provides flexibility to young plant parts like leaves and stems.  [NDA 2012-I]

• Living cells
• Unevenly thickened cell walls at corners
• Provides mechanical support without rigidity

Flexibility of leaf and stem is attributed to an abundance of collenchyma.  [NDA 2012-I]

Sclerenchyma: Dead, Rigid Support

Sclerenchyma provides rigidity and strength.  [NDA 2020]

• Dead cells at functional maturity: most tested fact about sclerenchyma
• Thick, lignified (hardened) cell walls
• No protoplast (living contents) at maturity

Sclerenchyma is usually without protoplast and is regarded as dead cells.  [NDA 2026-I]

Simple Permanent Tissue Summary

Tissue	Living or Dead?	Key Property
Parenchyma	Living	Thin walls; intercellular spaces; packing tissue
Chlorenchyma	Living	Parenchyma with chloroplasts; photosynthesis  [NDA 2013-I]
Aerenchyma	Living	Parenchyma with air sacs; buoyancy in aquatics  [NDA 2022-I]
Collenchyma	Living	Corner-thickened walls; flexibility  [NDA 2012-I]
Sclerenchyma	DEAD	Lignified walls; rigidity; no protoplast  [NDA 2020 | NDA 2026-I]

Fruit Softening

Softening of mature ripe fruits is due to the dissolution of the middle lamella, as the pectin-rich layer between cells breaks down as the fruit ripens.  [NDA 2009-II] Not degradation of primary wall, not delignification, not removal of suberin.

5. Complex Permanent Tissues: Xylem and Phloem

Xylem: Water Transport

Xylem transports water and dissolved minerals from roots to all parts of the plant (upward conduction). Xylem consists of four components: tracheids, vessels, xylem parenchyma, and xylem fibres.  [NDA 2019-II]

Component	Living or Dead?	Function
Tracheids	Dead	Water conduction; support
Vessels	Dead	Main water-conducting elements
Xylem parenchyma	LIVING	Lateral transport; storage  [NDA 2019-III | CDS 2023-I]
Xylem fibres	Dead	Mechanical support

★ IMPORTANT

Xylem does NOT consist of sieve plate, sieve tube, and companion cells: those belong to phloem.  [NDA 2019-II]

Among all xylem components, only xylem parenchyma is LIVING. Tracheids, vessels, and xylem fibres are all dead.

Flexibility is NOT due to sclerenchyma: flexibility comes from collenchyma.  [NDA 2019-II]

Phloem: Food Transport

Phloem transports organic food (sugars) from leaves to other parts of the plant. The inner bark of a woody plant transports food from the leaves to the other parts of the plant.  [NDA 2011-II]

The inner bark does NOT transport minerals from roots (that is xylem), does NOT act as an impermeable membrane.

Pericycle: NOT a Conducting Tissue Component

The pericycle is NOT a component of conducting tissue in plants.  [NDA 2019-I] Fibres  (in xylem and phloem), Tracheids  (xylem), Sieve tubes  (phloem): all are conducting tissue. Pericycle is outside the vascular bundle in roots: not part of the conducting system.

6. Flower Structure

A typical flower has four whorls attached to the thalamus (receptacle):

• Sepals: outermost; usually green; protect the bud.
• Petals: colourful; attract pollinators.
• Stamens: male reproductive organs. Each has a filament and an anther. The anther produces pollen grains.
• Carpel/Pistil (Gynoecium): female. Each carpel has: Stigma (sticky tip), Style (connecting tube), Ovary (swollen base containing ovules).

Stamen, Pollen, and Flower Anatomy Facts

Pollen grains are produced in the anther: NOT in the ovary.  [NDA 2013-I]

Stamen is NOT present in the centre of a flower. The carpel occupies the centre. Stamens form a whorl around the central carpel.  [NDA 2013-I]

The swollen bottom part of the carpel is the ovary.  [NDA 2013-I]

The fusion of germ cells gives rise to the zygote.  [NDA 2013-I]

Sunflower and Marigold: Inflorescence, Not a Single Flower

The colourful head of sunflower or marigold is an inflorescence, not a single flower.  [NDA 2017-I] A sunflower “head” is a compact cluster of hundreds of individual flowers (florets). The structure is called an inflorescence (capitulum).

Unisexual vs Bisexual Flowers

Type	Contains	Examples
Bisexual	Both stamen and carpel	Hibiscus, Mustard, Sunflower
Unisexual	Either stamen or carpel: not both	Papaya has unisexual flowers [NDA 2022-I]

7. Pollination

Pollination is the transfer of pollen grains from the anther to the stigma. It is NOT fertilisation. Pollen transfer is only the first step.

Honey bees visiting flowers help with pollination: not faster development, not pollen germination, not flower size increase.  [NDA 2023-II]

8. Pollen Germination and Pollen Tube Pathway

The correct sequence of the pollen tube pathway: Stigma → Style → Ovary.  [NDA 2021-I]

Stigma  →  Style  →  Ovary

DNA content is halved during pollen formation, because pollen is produced through meiosis.  [NDA 2023-II] Not during seed germination, fruit formation, or flower bud formation.

The pollen tube enters the ovule through a small pore called the micropyle. Chalaza is the ovule base; funicle is the stalk; integument forms the seed coat.

9. Double Fertilisation: Syngamy and Triple Fusion

Double fertilisation is unique to angiosperms. Two fusion events occur simultaneously inside the ovule.

★ IMPORTANT

Syngamy: one male gamete (N) fuses with the egg cell (N) → forms the zygote (2N: diploid).

Triple fusion: the other male gamete (N) fuses with the diploid secondary nucleus (2N) → forms the primary endosperm nucleus (3N: triploid).

Both gametes are used: neither degenerates. Neither fuses with a second egg cell.  [NDA 2023-II]

Zygote = 2N (Diploid); Endosperm = 3N (Triploid) in a diploid plant.  [NDA 2018-II]

Gametophytes of sexually reproducing flowering plants are haploid (N).  [NDA 2015-I]

Event	Components	Result	Ploidy
Syngamy	Male gamete (N) + Egg cell (N)	Zygote	2N (Diploid)  [NDA 2018-II | NDA 2023-II]
Triple Fusion	Male gamete (N) + Secondary nucleus (2N)	Endosperm nucleus	3N (Triploid)  [NDA 2018-II | NDA 2023-II]

10. Seed Formation

Correct sequence in sexual reproduction: Egg → Zygote → Embryo → Seed.  [NDA 2023-II]

• Zygote → divides repeatedly → Embryo
• Primary endosperm nucleus → Endosperm (food reserve)
• Ovule → Seed

Seeds of flowering plants are made up of: Embryo, food reserves, and seed coat.  [NDA 2015-I] Not simply the ovary wall. Not cotyledons alone. Not zygotes alone.

The nucellus is the part of the ovule that possesses reserve food.  [NDA 2026-I] Not the integument (forms seed coat), not the funicle (stalk), not the chalaza (base region).

11. Fruit Formation

★ IMPORTANT

Ovary → Fruit; Ovule → Seed  [NDA 2022-II | NDA 2023-II]

This is the single most persistently confused mapping in plant reproduction.

Ovary produces the fruit. Ovule produces the seed. NOT the reverse.

True Fruit vs False Fruit

Type	Develops From	Examples
True fruit	Only from the ovary	Date, Grape, Plum
False fruit (accessory fruit)	Partly from other floral parts in addition to or instead of the ovary	Apple: fleshy part from thalamus  [NDA 2010-I | NDA 2026-I]

Apple is a false fruit. The fleshy edible part develops from the thalamus (receptacle): not from the ovary. The ovary forms only the core.  [NDA 2010-I | NDA 2026-I]

12. Seed Germination

Embryo Part	Develops Into
Radicle	The root  [NDA 2021-I]: “R to R”
Plumule	The shoot (leaves and stem above ground): “P to Plant”
Cotyledons	Seed leaves that store food for the seedling

13. Vegetative Propagation

Vegetative propagation through eye buds takes place in potato.  [NDA 2024-II]

Plant	Propagation Structure
Potato	Eye buds (tuber buds)  [NDA 2024-II]
Ginger	Rhizome
Onion	Bulb
Sugarcane	Stem cuttings

Saffron is obtained from the dry stigma of the saffron plant (Crocus sativus).  [NDA 2009-II] Not from leaves, not from fruits, not from petals.

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