Ch 3 · Sexual Reproduction in Plants · IGCSE Biology 0610
Topic 3 of 5 in Reproduction — IGCSE Biology 0610 — 58 lessons.
Introduction
A flower is a plant's reproductive organ, arranged so that pollen from the stamens reaches a stigma, carried by an insect or by the wind. A pollen tube must then grow down to the ovule so that the nuclei can fuse. This lesson covers flower structure, insect- and wind-pollinated flowers, pollination, fertilisation and germination.
Key ideas — Parts of an insect-pollinated flower and their functions
When drawing, use single clear lines, no shading, label lines touching the structure, and show ovules inside the ovary.
🧑🏫 Teacher's explanation
Think of an insect-pollinated flower as a high-tech trap designed to trick a bee into doing its job. The flower doesn't just sit there; it actively recruits a worker. The bright petals are the advertisement, the nectary is the payment, and the sticky stigma is the collection point. If the flower fails to attract the insect, the reproductive cycle stops. This is a biological transaction: the plant provides food, and the insect provides transport for the genetic material.
📖 Definitions
🔍 Worked example — Easy
Identify the part of the flower that produces the male gametes and state its specific function.
🔍 Worked example — Standard
Explain why the stigma of an insect-pollinated flower is often sticky or feathery.
🔍 Worked example — Exam-style
Compare the structural adaptations of insect-pollinated and wind-pollinated flowers, focusing on the stigma and anthers.
⚠️ Common errors
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🎯 Exam question
(a) Identify the parts labelled A, B, and C.
Key ideas — Insect-pollinated versus wind-pollinated flowers
Wind-pollinated flowers (grasses, many trees) need not attract insects; they are adapted to release and catch airborne pollen.
🧑🏫 Teacher's explanation
Think of pollination as a delivery service. Insect-pollinated flowers are like high-end boutiques: they use bright colors, sweet scents, and nectar (the 'payment') to attract specific 'couriers' (insects) to carry pollen directly to another flower. Because the insect travels from flower to flower, this usually results in cross-pollination, which increases genetic variation.
📖 Definitions
🔍 Worked example — Easy
A student observes two flowers. Flower A has large, brightly colored petals and a sticky stigma. Flower B has small, green petals and a feathery stigma. Identify the pollination method for each flower.
🔍 Worked example — Standard
Compare the pollen grains of an insect-pollinated flower and a wind-pollinated flower in terms of size and texture.
🔍 Worked example — Exam-style
A plant species relies solely on self-pollination. Explain one disadvantage of this method in terms of genetic variation.
⚠️ Common errors
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🎯 Exam question
(a) Identify the most likely pollination method for Plant X and Plant Y. [2] (b) Explain how the structure of the stigma in Plant Y is adapted to its pollination method. [2] [4 marks]
Key ideas — Pollination: self and cross
Pollination is the transfer of pollen grains from an anther to a stigma.
🧑🏫 Teacher's explanation
Think of pollination as the biological version of sending a letter. The pollen grain is the letter, the anther is the mailbox where it's sent from, and the stigma is the recipient's mailbox. For a plant to produce seeds, that letter must reach the right destination.
📖 Definitions
🔍 Worked example — Easy
A student observes a flower where the pollen grains from the anther have landed on the stigma of the same flower. Identify the type of pollination occurring.
🔍 Worked example — Standard
Compare the genetic implications of cross-pollination versus self-pollination in a population of plants.
🔍 Worked example — Exam-style
A farmer notices that his crop of self-pollinating wheat is being destroyed by a specific fungal pathogen. Explain why this crop is more at risk than a crop that undergoes cross-pollination.
⚠️ Common errors
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🎯 Exam question
(a) Define pollination. [1] (b) Explain why a decrease in the bee population would lead to a decrease in the seed set of this plant species. [2] [3 marks]
Key ideas — Pollen tube growth and fertilisation
The zygote becomes the embryo, the ovule the seed, and the ovary the fruit. Pollination is the arrival of pollen; fertilisation is the fusion of nuclei inside the ovule.
🧑🏫 Teacher's explanation
Think of pollination as the delivery of a letter and fertilisation as the actual reading and understanding of that letter. Just because the letter has arrived at the house (the stigma) doesn't mean the message has been processed. The pollen tube acts like a specialized delivery tunnel, carving a path through the plant's tissue to ensure the genetic material reaches its destination safely.
📖 Definitions
🔍 Worked example — Easy
A student observes a flower and notes that pollen grains from the anther of one plant have landed on the stigma of a different plant of the same species. State the type of pollination occurring and explain one potential advantage of this process.
🔍 Worked example — Standard
Describe the pathway taken by the male gamete nucleus from the surface of the stigma to the fusion with the female gamete.
🔍 Worked example — Exam-style
A researcher calculates that in a specific population of plants, the rate of successful fertilisation decreases as the distance between individual plants increases. Explain why this occurs in terms of pollination types.
⚠️ Common errors
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🎯 Exam question
Key ideas — Conditions for germination
Germination needs three conditions:
🧑🏫 Teacher's explanation
Think of a seed like a tiny, sleeping biological machine. It is currently in a state of dormancy, meaning it is 'paused' to survive harsh conditions. To 'wake up' and start growing, it needs a specific set of keys to turn the engine on.
📖 Definitions
🔍 Worked example — Easy
A student investigates germination. In a petri dish with water, oxygen, and a temperature of 25 circC, 8 out of 10 seeds germinate. In a dish with water, oxygen, and a temperature of 4 circC, 0 out of 10 seeds germinate. Calculate the percentage change in germination success between the two conditions.
🔍 Worked example — Standard
Explain why a seed placed in boiled, cooled water with a layer of oil on top fails to germinate.
🔍 Worked example — Exam-style
A student uses 50 seeds in each of three test tubes. Tube 1: Water, Air, 25 circC. Tube 2: Dry, Air, 25 circC. Tube 3: Water, Air, 25 circC. Tube 3 is a duplicate of Tube 1. Describe how this experiment could be used to identify the variables and state why Tube 3 is necessary.
⚠️ Common errors
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🎯 Exam question
Worked example
(a) The pollen grain germinates and grows a pollen tube [B1]; the tube grows down through the style to the ovary [B1]; it enters the ovule through the micropyle [B1]; the male gamete nucleus passes down the tube and fuses with the female gamete (egg cell) nucleus to form a zygote [B1].
🔍 Worked example — Easy
A student observes a flower and identifies the following parts: a sticky top surface (stigma), a long stalk (style), a swollen base (ovary), and small structures inside the ovary (ovules). Identify the reproductive organ being described and state its primary function.
🔍 Worked example — Standard
Compare the structural adaptations of an insect-pollinated flower versus a wind-pollinated flower regarding their petals and anthers.
🔍 Worked example — Exam-style
A plant produces 5,000 pollen grains. Only 12 grains successfully reach a stigma and undergo fertilisation. Calculate the percentage of pollen grains that successfully resulted in fertilisation.
⚠️ Common errors
Common mistakes
Practice
Questions