The Flower ICSE Class 9: Structure of a Bisexual Flower, Whorls and Their Functions

What The Flower is about

Weightage: CISCE publishes no chapter weightage for ICSE Biology. The Flower is topic 2, Flowering Plants (i), of the Class IX part of the 2028 syllabus; the Class IX paper (80 marks, 2 hours) is set and marked by the school.Source: CISCE ICSE Biology (Science Paper 3) syllabus, examination year 2028 (Class IX)

Key concepts

Parts of a typical bisexual flower

From outside to inside, a flower such as hibiscus (china rose) or mustard shows:

• Pedicel: the stalk of the flower.
• Thalamus (receptacle): the swollen tip of the pedicel on which the whorls are attached.
• Calyx: the outermost whorl of sepals (usually green).
• Corolla: the whorl of petals (usually coloured).
• Androecium: the male whorl of stamens.
• Gynoecium (pistil): the innermost, female whorl of carpels.

A bisexual (hermaphrodite) flower has both androecium and gynoecium (hibiscus, mustard, pea). A unisexual flower has only one: staminate (male) or pistillate (female), as in papaya, maize and cucumber.

When calyx and corolla look alike (as in lily and onion), together they are called the perianth, and each member a tepal.

Worked example

A papaya plant bears flowers with only stamens. Is the flower bisexual or unisexual? Can this plant produce fruit on its own?

Try it first, then show the solutionSolution

1. It has only the androecium: unisexual (staminate, male).
2. Fruits form from ovaries, which are in the gynoecium; this plant has none.

Answer: Unisexual male; it cannot produce fruit itself.

Non-essential (accessory) whorls: calyx and corolla

They are called non-essential because they do not take part directly in reproduction, but they help it.

Calyx (sepals):

• Protects the inner parts of the flower in the bud stage.
• If green, carries out photosynthesis.
• In some flowers, coloured sepals attract insects; in some, hairy sepals help in dispersal of fruits (e.g. pappus).
• Sepals may be free (polysepalous) or joined (gamosepalous).

Corolla (petals):

• Attracts insects and other pollinators by colour, scent and nectar (nectaries often at the base of petals).
• Protects the essential whorls.
• Provides a landing platform for insects.
• Petals may be free (polypetalous) or joined (gamopetalous).

Worked example

Why are the petals of night-blooming flowers like jasmine often white and strongly scented?

Try it first, then show the solutionSolution

1. They are pollinated by moths active at night.
2. White shows up in dim light, and strong scent guides moths in the dark.

Answer: To attract night-flying pollinators.

Essential whorls: androecium

Androecium = all the stamens (the male reproductive organs; each stamen is a microsporophyll).

Each stamen has:

• Filament: a thin stalk that holds the anther up in a good position for pollination.
• Anther: a two-lobed head, usually with four pollen sacs, which produce pollen grains by meiosis. Pollen grains form the male gametes.
• Connective: the tissue joining the two anther lobes to the filament.

When ripe, the anther dehisces (splits open) to release pollen.

In hibiscus, the filaments are fused into a staminal tube around the style (monadelphous); in mustard there are six stamens, four long and two short.

Worked example

Name the part of a stamen that (a) produces pollen, (b) supports the anther, (c) joins the anther lobes.

Try it first, then show the solutionSolution

1. (a) Anther (pollen sacs).
2. (b) Filament.
3. (c) Connective.

Answer: Anther, filament, connective.

Essential whorls: gynoecium (pistil)

Gynoecium = all the carpels (the female reproductive organs; each carpel is a megasporophyll). One or more carpels form the pistil.

Each carpel has:

• Stigma: the tip; often sticky or feathery to receive pollen.
• Style: a stalk through which the pollen tube grows down to the ovary.
• Ovary: the swollen base containing ovules, attached to a cushion of tissue, the placenta. Each ovule contains an embryo sac with the egg cell (female gamete).

After fertilisation, the ovary becomes the fruit and the ovules become seeds.

Carpels may be free (apocarpous, as in lotus, rose) or fused (syncarpous, as in hibiscus, mustard, tomato).

Worked example

Which part of the flower becomes (a) the fruit, (b) the seed? (c) Which part receives the pollen?

Try it first, then show the solutionSolution

1. (a) Ovary.
2. (b) Ovule.
3. (c) Stigma.

Answer: Ovary → fruit; ovule → seed; stigma receives pollen.

Complete and incomplete flowers

Complete flower	Incomplete flower
has all four whorls: calyx, corolla, androecium, gynoecium	lacks one or more of the four whorls
always bisexual	may be bisexual (e.g. lacking petals) or unisexual
e.g. hibiscus, mustard, pea, rose	e.g. maize and papaya (unisexual); flowers with no petals

Note: every unisexual flower is incomplete, since it lacks one essential whorl. A bisexual flower is not necessarily complete: it may lack sepals or petals.

Regular (actinomorphic) flowers can be cut into two equal halves along more than one plane (mustard, hibiscus); irregular (zygomorphic) flowers only along one plane (pea).

Worked example

A flower has stamens and carpels but no petals or sepals. Is it bisexual? Is it complete?

Try it first, then show the solutionSolution

1. It has both essential whorls: bisexual.
2. It lacks the calyx and corolla: incomplete.

Answer: Bisexual but incomplete.

Inflorescence and placentation (meaning only)

Inflorescence: the arrangement of flowers on the floral axis (the main stalk, called the peduncle). A flower borne singly is a solitary flower (hibiscus); many flowers grouped on one axis form an inflorescence (mustard, sunflower head, grape bunch). Grouping makes the flowers more conspicuous to pollinators.

Placentation: the arrangement of ovules on the placenta inside the ovary. Examples: in a pea pod the seeds lie in a row along one edge of the ovary (marginal); in a tomato or orange, cut across, the seeds are attached to the central axis between the chambers (axile).

(The syllabus asks for the meaning of these terms only, not their detailed types.)

Worked example

Define inflorescence and placentation in one line each.

Try it first, then show the solutionSolution

1. Inflorescence: arrangement of flowers on the floral axis.
2. Placentation: arrangement of ovules on the placenta within the ovary.

Answer: As above.

The Flower in real life

Each concept, met in an everyday situation. Read the situation, answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

Topics in this chapter

• Parts of a Flower and Their Functions

The Flower: key facts

Whorls from outside

$\text{calyx}\to \text{corolla}\to \text{androecium}\to \text{gynoecium}$

On the thalamus.

Stamen

$\text{stamen}=\text{filament}+\text{anther}(+\text{connective})$

Male organ.

Carpel

$\text{carpel}=\text{stigma}+\text{style}+\text{ovary (ovules)}$

Female organ.

After fertilisation

$\text{ovary}\to \text{fruit};\text{ovule}\to \text{seed}$

Link to Fertilisation.

The Flower: diagrams to practise

Practise each one on paper: draw it from the checklist, then tick off every label.

How the school exam asks The Flower

The question patterns to expect, and the method that works for each.

Tricks to remember The Flower

Short memory aids. Say each one aloud once, then use it on a question the same day.

• 'Can Children Ask Grandma?'

  Calyx, Corolla, Androecium, Gynoecium: outside to inside.

  Use it when: Order of whorls.

• Andro = man, Gyno = woman

  Androecium male (stamens), gynoecium female (carpels).

  Use it when: Which whorl is which.

• S-S-O down the pistil

  Stigma (catches), Style (tube), Ovary (seeds-to-be).

  Use it when: Parts of a carpel.

• Every unisexual flower is incomplete

  Missing one essential whorl means missing a whorl.

  Use it when: Complete versus incomplete.

The Flower: exam-level solved questions

Ordered from exam level to HOTS. Cover the solution, write your own, then compare step by step.

Case-study practice (Section B style)

Read the situation, then answer every part. In a school exam set on the board pattern this is a 5-mark question split into 2 + 1 + 1 + 1 marks.

Where the marks are

How a typical answer is split into step marks. Show every step: a right final answer alone rarely earns full marks.

Where students lose marks in The Flower

The slips examiners see most often, and what to write instead.

• ✗Mistake: Pistil and stamen swapped

  Students guess which is male and which is female.

  Wrong working

  The stamen is the female part.

  Right working

  Stamen (androecium) is male; carpel/pistil (gynoecium) is female.

  ✓Do this: Andro = male.

  Usually costs: 1 mark.

• ✗Mistake: Complete equated with bisexual

  The two terms are confused.

  Wrong working

  A bisexual flower is a complete flower.

  Right working

  Complete = all four whorls; bisexual = both stamens and carpels. A bisexual flower may be incomplete.

  ✓Do this: Complete counts four whorls; bisexual counts two.

  Usually costs: 1 mark.

• ✗Mistake: Writing types of placentation or inflorescence in detail

  The syllabus asks for meaning only; long lists waste time and invite errors.

  Wrong working

  A page on racemose and cymose types.

  Right working

  One-line meaning with a simple example.

  ✓Do this: Meaning plus one example.

  Usually costs: Time.

• ✗Mistake: Labels pointing to the wrong part

  In an L.S. drawing, label lines end in empty space or on the wrong whorl.

  Wrong working

  'Ovary' line ending on the thalamus.

  Right working

  Ruled line touching the swollen ovary above the thalamus.

  ✓Do this: End each label line exactly on the part.

  Usually costs: 1/2 mark per label.

Practice questions on The Flower

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

1. Q1 · 1 mark · MCQExam level

   Pollen grains are produced in the:
   (a) stigma
   (b) ovary
   (c) anther
   (d) filament

   Hint

   Male part.

   Answer

   (c)

2. Q2 · 1 mark · MCQExam level

   A flower lacking the androecium is:
   (a) bisexual and complete
   (b) unisexual and incomplete
   (c) bisexual and incomplete
   (d) unisexual and complete

   Hint

   Female only.

   Answer

   (b)

3. Q3 · 2 marks · Very short answerExam level

   Name: (a) the stalk of the flower, (b) the swollen base of a carpel, (c) the tissue joining anther lobes, (d) the cushion in the ovary to which ovules are attached.

   Hint

   Pedicel...

   Answer

   (a) Pedicel (b) Ovary (c) Connective (d) Placenta

4. Q4 · 2 marks · Short answerExam level

   Give two functions of the corolla.

   Hint

   Attract, protect.

   Answer

   Attracts pollinators by colour, scent and nectar; protects the essential whorls (also gives a landing platform).

5. Q5 · 2 marks · Short answerHarder exam level

   Distinguish between polysepalous and gamosepalous calyx, and between apocarpous and syncarpous gynoecium.

   Hint

   Free versus fused.

   Answer

   Polysepalous: sepals free; gamosepalous: sepals fused. Apocarpous: carpels free; syncarpous: carpels fused.

6. Q6 · 2 marks · Short answerHarder exam level

   Why is a stigma often sticky or feathery? Why is the style often long?

   Hint

   Catching pollen.

   Answer

   A sticky or feathery stigma traps pollen grains easily. A long style holds the stigma in a position where pollen is likely to reach it (e.g. above the anthers or out in the wind).

7. Q7 · 3 marks · Short answerHarder exam level

   A flower has 5 sepals, 5 petals, 10 stamens and one carpel, but the stamens shrivel before the stigma is ready. (a) Is it complete? (b) Can it fertilise itself? Explain.

   Hint

   Timing.

   Answer

   (a) Yes: all four whorls present. (b) Not normally: by the time its stigma is ready, its own pollen is no longer available, so it needs pollen from another flower.

8. Q8 · 2 marks · Short answerHarder exam level

   What is meant by an inflorescence? Give one advantage of flowers being grouped in an inflorescence.

   Hint

   Visibility.

   Answer

   The arrangement of flowers on a floral axis. Grouped flowers are more conspicuous to pollinators, and one insect visit can pollinate many flowers.

9. Q9 · 3 marks · Short answerHarder exam level

   Explain why calyx and corolla are called accessory whorls though a flower without petals may never be pollinated by insects.

   Hint

   Direct versus indirect.

   Answer

   They do not produce gametes and do not take part directly in fertilisation, so they are accessory. They help indirectly: sepals protect the bud and petals attract insect pollinators, so an insect-pollinated flower without petals may not be visited.

10. Q10 · 3 marks · Short answerHOTS / competency

    A tomato is cut across and the seeds are seen attached to the central axis in several chambers. (a) Which part of the flower was the tomato? (b) What were the seeds? (c) What term describes their arrangement, and how many carpels probably fused to form it if there are three chambers?

    Hint

    One chamber per carpel.

    Answer

    (a) The ovary. (b) Ovules (fertilised). (c) Placentation (axile); about three carpels fused.

11. Q11 · 3 marks · Short answerHOTS / competency

    A gardener notices that cucumber vines produce two kinds of flowers, and only one kind develops a tiny cucumber behind the petals. Explain, using the terms unisexual, staminate and pistillate, and say why both kinds are needed.

    Hint

    Ovary behind the petals.

    Answer

    Cucumber flowers are unisexual. Pistillate (female) flowers have an ovary (the tiny cucumber) and develop into fruit. Staminate (male) flowers have only stamens and supply pollen. Pollen from male flowers must reach female flowers for fruit to form.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1. 1.Outermost whorl of a flower?Show answer

   Calyx (sepals).

2. 2.Male whorl?Show answer

   Androecium (stamens).

3. 3.Part of the carpel that receives pollen?Show answer

   Stigma.

4. 4.Part that becomes the seed?Show answer

   Ovule.

5. 5.Calyx and corolla together, when alike?Show answer

   Perianth (tepals).

6. 6.Name a unisexual flower.Show answer

   Papaya, maize or cucumber.

7. 7.Meaning of placentation?Show answer

   Arrangement of ovules on the placenta in the ovary.

8. 8.Stalk of a flower?Show answer

   Pedicel.

Quick revision checklist

The night before the exam: can you do each of these without looking?

• ☐Can you name all the parts of a flower from pedicel to stigma?
• ☐Can you give one function of every part?
• ☐Can you explain why two whorls are 'essential'?
• ☐Can you classify any flower as complete or incomplete, bisexual or unisexual?
• ☐Can you define inflorescence and placentation?
• ☐Can you draw and label the L.S. of a flower?

The Flower: frequently asked questions