Plant Kingdom and Plant Growth and Development: Groups, Growth and Hormones for NEET by Physics Wallah

Many NEET students find the plant kingdom hard because it has five groups that look alike on paper. Algae and bryophytes get mixed up, pteridophytes and gymnosperms share traits, and plant hormones have many names and roles. Growth curves and terms like differentiation and plasticity add more confusion.

The sections below start with the five plant groups and how they are classified. They then move to growth and development and end with plant growth regulators. Each part is short and easy to scan. PW’s online Biology classes can help you practise the same chapter with notes and tests.

What Is the Plant Kingdom?

The plant kingdom is a core area of biology, and our understanding of it has changed over time. Knowing how the groups were separated makes the rest of the chapter easier to place.

R.H. Whittaker’s Five Kingdom Classification (1969) divided living things into Monera, Protista, Fungi, Plantae and Animalia. Earlier, Carolus Linnaeus used a Two-Kingdom System. It placed all organisms with a cell wall in Plantae, including bacteria and fungi. Modern classification removed these groups and treats Monera, Protista and Fungi as separate kingdoms.

Kingdom Plantae now has five groups, listed from simple to complex:

1. Algae: The simplest plants.

2. Bryophytes

3. Pteridophytes

4. Gymnosperms

5. Angiosperms: The most complex group, the flowering plants with flowers and fruits.

How Are Angiosperms Classified?

Angiosperms are the most complex and dominant plant group. Their seeds are protected by a seed coat and a fruit. Three systems are used to classify them.

• Artificial system (Carolus Linnaeus): It is based on superficial features, both vegetative and sexual. It gave equal weight to vegetative characters, which change with the environment, and sexual characters, which stay constant. This made it unreliable.

• Natural system (Bentham and Hooker): It uses natural affinities, with features such as morphology, anatomy, embryology and phytochemistry. It is better than the artificial system.

• Phylogenetic system (Engler and Prantl): It is based on evolutionary relationships and common ancestry. It is the most accepted system today.

Modern taxonomy also uses special tools:

• Cytotaxonomy: Uses cytological information such as chromosome number, structure and behaviour.

• Chemotaxonomy: Uses chemical constituents such as biomolecules and secondary metabolites.

• Numerical taxonomy: Gives numbers and codes to all observable characters so a computer can compare many features. Its limit is that it gives equal importance to every character.

Comparing the Five Plant Groups

A comparison makes the five groups easier to revise. The table below sets them side by side on body level, vascular tissue, main plant body and life cycle. Read it row by row, because exam questions often pick one feature.

Algae: Uses, Reproduction and Classes

Algae are the simplest plants. They have a thalloid body with no true roots, stems or leaves. They are green and make their own food through photosynthesis. Most live in water, in freshwater or the sea, and they prefer moist places. Their form varies widely, from unicellular Chlamydomonas to colonial Volvox, filamentous Spirogyra and giant kelps of up to 100 metres.

Why Are Algae Important?

• Oxygen: They raise oxygen levels.

• Food chains: They are primary producers in aquatic food chains.

• Food: More than 70 species are edible, such as Laminaria, Porphyra and Sargassum.

• Carbon fixation: They do at least half of the total CO₂ fixation on Earth.

• Hydrocolloids: Brown algae give algin, and red algae give carrageenan. Agar comes from the red algae Gelidium and Gracilaria and is used in culture media and food. Memory tip: algin from brown (A-B), carrageenan from red (R-R).

• Protein: Chlorella is a compact protein source and is used by space travellers.

How Do Algae Reproduce?

• Vegetative: Mainly by fragmentation, as in Spirogyra.

• Asexual: Usually through motile zoospores.

• Sexual: By the fusion of gametes, in three ways:

• Isogamous: The gametes look alike. They may have flagella, as in Ulothrix, or not, as in Spirogyra.

• Anisogamous: The gametes look different, as in Eudorina.

• Oogamous: The female gamete is large and non-motile, and the male gamete is small and motile, as in Volvox and Fucus. Memory tip: “O” in oogamous links to ovum.

Classes of Algae

Algae fall into three classes: Chlorophyceae (green), Phaeophyceae (brown) and Rhodophyceae (red). The sequence runs from simpler to more complex forms. The table below compares the three classes. Focus on pigments and stored food, as these are asked most often.

Three more points are worth remembering:

• Pyrenoids in green algae have a protein core with a starch sheath. Memory tip: protein inside, starch outside.

• Brown algae have a holdfast for anchorage, a stem-like stipe and a leaf-like frond.

• Red algae live at great depths because phycoerythrin absorbs the blue-violet light that reaches deep water. They show complex post-fertilisation events.

Bryophytes and Their Life Cycle

Bryophytes grow in moist, shady places. They are called the amphibians of the plant kingdom because they live on land but need water for sexual reproduction. The body, or thallus, can be prostrate or erect. It has root-like rhizoids, which are unicellular in liverworts and multicellular in mosses.

Why Are Bryophytes Useful?

• Some mosses give food to animals.

• Peat moss (Sphagnum) gives peat, which is used as fuel. It also holds a lot of water, so it is used as packing material.

• Bryophytes grow first on bare ground and so help in plant succession and soil formation.

Life Cycle of Bryophytes

1. The main plant body is the haploid (n) gametophyte. It is dominant, photosynthetic and independent.

2. The antheridium makes biflagellated antherozoids, and the archegonium makes a single egg.

3. Water is needed for antherozoids to reach the egg. Fusion forms a diploid (2n) zygote.

4. The zygote grows into a diploid sporophyte, which stays attached to the gametophyte and takes food from it.

5. Cells of the sporophyte divide by meiosis to make haploid (n) spores.

6. Spores germinate into a new gametophyte.

Liverworts, such as Marchantia, grow in moist, shady places. The thallus is flat from top to bottom. They reproduce asexually by fragmentation or by gemmae, which are multicellular buds in gemma cups. The sporophyte has a foot, seta and capsule.

Mosses are more advanced than liverworts. Their gametophyte has two stages. The first is the protonema, a creeping, branched, filamentous stage that grows from a spore. The second is the leafy stage, which grows from lateral buds on the protonema. It has spirally arranged leaves and multicellular rhizoids, and it bears the sex organs. The moss sporophyte is more elaborate and has better spore dispersal.

Pteridophytes: The First Vascular Plants

Pteridophytes include horsetails and ferns. They are the first land plants with vascular tissue (xylem and phloem). They have true roots, stems and leaves, and they grow in cool, damp, shady places. They need water for reproduction.

• Uses: They bind soil and stop erosion; some have medicinal value (for example, Selaginella), and many are grown as ornamental plants.

• Leaves: Microphylls are small, as in Selaginella. Macrophylls are large, as in ferns.

• Cones (strobili): Compact, cone-like groups of sporophylls, as in Selaginella and Equisetum.

• Heterospory: Some make two kinds of spores. Microspores give male gametophytes, and megaspores give female gametophytes, as in Selaginella and Salvinia.

• Seed habit link: The female gametophyte stays on the parent sporophyte for some time, and the young sporophyte starts growing inside it. This is a step towards the seed habit, although pteridophytes do not form seeds.

Life Cycle of Pteridophytes

1. The main plant body is a diploid (2n) sporophyte, which is dominant and independent.

2. Sporangia on sporophylls make haploid (n) spores by meiosis.

3. Spores grow into a small, photosynthetic, haploid prothallus, which bears antheridia and archegonia.

4. Male gametes swim to the egg and form a diploid zygote.

5. The zygote grows into a new sporophyte, which at first depends on the gametophyte.

Pteridophytes are classified as follows:

• Psilopsida: Psilotum

• Lycopsida: Lycopodium, Selaginella (memory tip: “Life Science”)

• Sphenopsida: Equisetum

• Pteropsida: Pteris, Dryopteris, Adiantum

Gymnosperms: Plants with Naked Seeds

Gymnosperm means naked seed. These plants have no ovary and no fruit around the seeds. They are mostly shrubs or medium to tall trees, and Sequoia gigantica is one of the tallest trees.

• Roots: They have a tap root system. Pinus roots form mycorrhiza, a link with fungi. Cycas roots form coralloid roots with cyanobacteria, which fix nitrogen. Memory tip: C for Cycas, C for coralloid roots, C for cyanobacteria.

• Stem: Unbranched in Cycas and branched in Pinus and Cedrus.

• Leaves: Pinnate in Cycas and needle-like in Pinus.

• Water saving: Leaves have a small surface area, sunken stomata and a thick cuticle.

Life Cycle of Gymnosperms

Gymnosperms are heterosporous. They make microspores, which become the male gametophyte, and megaspores, which become the female gametophyte. Memory tip: micro is small (male), and mega is large (female).

• Male cones carry microsporangia, which make microspores (pollen grains).

• Female cones carry megasporangia, and only one megaspore in each ovule stays functional.

• Wind carries pollen to the female cone. Fertilisation gives a zygote, and the embryo forms inside the seed.

• The diploid sporophyte is dominant, and the gametophytes depend on it.

Plant Growth and Development: Meaning and Features

Growth and development are different things. Growth is an irreversible, permanent increase in size, such as mass, surface area, volume or cell number. It can be measured, and anabolism is greater than catabolism. Development covers the whole life of the plant, from seed germination to senescence. It includes both growth and differentiation.

Plant growth has these features:

• Indeterminate (unlimited) growth: It goes on because shoot and root apical meristems keep dividing.

• Self-perpetuating meristematic cells: They keep supplying new cells.

• Open for differentiation: Cells show plasticity and can differentiate again.

• Primary growth: An increase in length from apical meristems.

• Secondary growth: An increase in girth from lateral meristems.

• Determinate growth: Some organs, such as leaves and flowers, grow to a fixed size.

Growth Phases, Growth Rate and Growth Curve

A growing region passes through three phases, one after another.

1. Meristematic phase: Cells divide actively at the tips.

2. Elongation phase: Cells grow longer, mainly by vacuolation.

3. Maturation phase: Cells reach full size and differentiate.

Growth rate can be arithmetic or geometric. The table below compares them. Pay attention to the equations, since numerical questions use them.

Geometric growth gives the sigmoid curve through a lag phase, a rapid growth phase and a stationary phase. Absolute and relative growth rates are also compared. The parallel line technique is used to find the zone of elongation in a root.

What Affects Plant Growth?

• External factors: Water, oxygen, nutrients, temperature, light and gravity. Water gives turgidity and supports metabolism, and oxygen supports respiration and ATP.

• Internal factors: Genetic material and hormones, which are plant growth regulators.

Differentiation and Plasticity in Plants

Cells can change form in three ways:

• Differentiation: Meristematic cells mature into specialised permanent cells.

• Dedifferentiation: Permanent cells gain the power to divide again. For example, medullary ray cells form interfascicular cambium.

• Redifferentiation: Dedifferentiated cells specialise again into new permanent cells. For example, interfascicular cambium forms secondary xylem and phloem.

Plasticity is the ability of plants to change the shape and size of their organs with the environment or with the stage of life. Heterophylly is one example, where a plant bears different kinds of leaves. The table below compares its two types. The key point is what triggers the change.

Memory tip: “Buttercup” (cup for water) for the environment, and “CCL” (cotton, coriander, larkspur) for life phase.

Plant Growth Regulators and Their Functions

Plant growth regulators (PGRs) are small, simple molecules that control body processes at very low concentrations. Auxins, gibberellins and cytokinins mainly promote growth. Abscisic acid (ABA) is an inhibitor. Ethylene plays both roles. The table below gives the chemical nature of each one, and it also shows the memory tips. Each regulator also has its own bioassay, so learn the test linked to each.

Important Plant Kingdom and Plant Growth Questions for NEET

Try each question on your own first, and then check your answer against the notes above.

Question 1 [2023-Manipur]

Which classes of algae possess pigment fucoxanthin and pigment phycoerythrin, respectively?

A. Phaeophyceae and Chlorophyceae
B. Phaeophyceae and Rhodophyceae
C. Chlorophyceae and Rhodophyceae
D. Rhodophyceae and Phaeophyceae

Question 2 [2022]

Which of the following is incorrectly matched?

A. Volvox - Starch
B. Ectocarpus - Fucoxanthin
C. Ulothrix - Mannitol
D. Porphyra - Floridean Starch

Question 3 [2022]

Hydrocolloid carrageen is obtained from:

A. Phaeophyceae only
B. Chlorophyceae and Phaeophyceae
C. Phaeophyceae and Rhodophyceae
D. Rhodophyceae only

Question 4 [2023]

Given below are two statements: One is labelled as Assertion A and the other is labelled as Reason R:

Assertion A: The first stage of gametophyte in the life cycle of moss is protonema stage.

Reason R: Protonema develops directly from spores produced in capsule.

In the light of the above statements, choose the most appropriate answer from the options given below:

A. A is not correct but R is correct.
B. Both A and R are correct and R is the correct explanation of A.
C. Both A and R are correct but R is NOT the correct explanation of A.
D. [Cut off in the screenshot. Add it from the video.]

Question 5 [2025]

The correct sequence of events in the life cycle of bryophytes is

A. Fusion of antherozoid with egg.
B. Attachment of gametophyte to substratum.
C. Reduction division to produce haploid spores.
D. Formation of sporophyte.
E. Release of antherozoids into water.

Choose the correct answer from the option given below:

A. D, E, A, C, B
B. B, E, A, C, D
C. B, E, A, D, C
D. D, E, A, B, C

Question 6 [2025]

Given below are the stages in the life cycle of pteridophytes. Arrange the following stages in the correct sequence.

A. Prothallus stage
B. Meiosis in spore mother cells
C. Fertilisation
D. Formation of archegonia and antheridia in gametophyte.
E. Transfer of antherozoids to the archegonia in presence of water.

Choose the correct answer from the options given below:

A. B, A, D, E, C
B. B, A, E, C, D
C. D, E, C, A, B
D. E, D, C, B, A

Question 7

In which one of the following, the ovules are not enclosed by an ovary wall and remain exposed?

(1) Selaginella
(2) Funaria
(3) Pinus
(4) Wolffia

Question 8 [2025]

Which one of the following is the characteristic feature of gymnosperms?

A. Seeds are enclosed in fruits.
B. Seeds are naked.
C. Seeds are absent.
D. Gymnosperms have flowers for reproduction.

Question 9

Heterophyllous development in response to environment is an example of which of the following phenomena?

(1) Dedifferentiation
(2) Elasticity
(3) Redifferentiation
(4) Plasticity

Question 10 [2025]

Which one of the following phytohormones promotes nutrient mobilization which helps in the delay of leaf senescence in plants?

A. Ethylene
B. Abscisic acid
C. Gibberellin
D. Cytokinin

Question 126

Match List I with List II:

Choose the correct answer from the options given below:

(1) A-IV, B-III, C-II, D-I
(2) A-I, B-II, C-IV, D-III
(3) A-III, B-I, C-IV, D-II

Once you can compare the five plant groups and match each hormone with its role, the plant kingdom and plant growth and development become much easier to revise. For regular practice with live classes and tests, you can explore PW NEET Batches.

Related Resources

• NEET Biology syllabus

• Class 12 Biology notes

• Reproduction in Organisms

• Plant Kingdom previous year questions

• NEET Biology important chapters

• NEET previous year question papers