This lesson covers:
- How fertilisation occurs in plants
- The development of seeds from ovules
- Different methods plants use to disperse seeds
Fertilisation in plants
In plants, the male gametes (sex cells) are contained within pollen grains, and they act like sperm in animals. The female gametes are found in the ovules. Each gamete contains a nucleus.
When pollen lands on a stigma:
- A tube called a pollen tube grows out and extends down through the flower’s style towards the ovary.
- A nucleus from the pollen grain moves down this tube to meet a nucleus in the female gamete (in an ovule inside the ovary).
- The male and female nuclei fuse together in a process called fertilisation, allowing genetic material to combine.
Seeds develop from ovules
After an egg cell is fertilised:
- The ovule matures into a seed containing an embryo plant and food supply.
- The food store provides nutrients to the embryo when the seed germinates.
- The ovary develops into a fruit around each seed.
Dispersal of seeds
Seed dispersal spreads out seeds so seedlings don’t compete for resources.
Common dispersal methods include:
- Wind – Blows seeds away e.g. dandelions, sycamores.
- Animals – Seeds excreted after fruits are eaten or seeds stick to fur e.g. blackberries.
- Explosions – Seed pods burst open flinging out seeds e.g. peas.
- Gravity – Fruits fall and roll away e.g. conkers.
Practice Quiz
1. How does fertilisation occur in plants?
Answer: Fertilisation in plants occurs when pollen grains land on a stigma. A pollen tube grows from the pollen grain down the style to the ovary, allowing the male gamete (pollen nucleus) to travel down the tube and fuse with the female gamete (egg cell) in the ovule.
2. What are male gametes in plants?
Answer: Male gametes in plants are contained within pollen grains, which act like sperm cells in animals.
3. What are female gametes in plants?
Answer: Female gametes in plants are found in the ovules, which are located inside the ovary of the flower.
4. What is the role of the pollen tube?
Answer: The pollen tube grows from the pollen grain down the style towards the ovary, providing a pathway for the male gamete to reach and fertilise the female gamete in the ovule.
5. What happens during the process of fertilisation in plants?
Answer: During fertilisation, the male gamete from the pollen grain fuses with the female gamete in the ovule, combining their genetic material to form a zygote.
6. What is the result of fertilisation in plants?
Answer: The result of fertilisation in plants is the formation of a zygote, which will develop into an embryo within the seed.
7. How do seeds develop from ovules?
Answer: After fertilisation, the ovule matures into a seed containing an embryo and a food supply. The surrounding ovary develops into a fruit that encases the seed.
8. What are the main parts of a seed?
Answer: The main parts of a seed are the seed coat (protective outer layer), the food store (provides nutrients), and the embryo (young plant).
9. What is the function of the seed coat?
Answer: The seed coat protects the seed from physical damage and prevents desiccation, ensuring the seed remains viable until conditions are right for germination.
10. What is the role of the food store in a seed?
Answer: The food store in a seed provides the necessary nutrients to support the growth and development of the embryo during germination.
11. What is seed dispersal?
Answer: Seed dispersal is the process by which seeds are spread away from the parent plant to reduce competition and increase the chances of successful germination and growth.
12. Why is seed dispersal important for plants?
Answer: Seed dispersal is important because it helps prevent overcrowding, reduces competition for resources, and allows plants to colonize new areas.
13. What are some common methods of seed dispersal?
Answer: Common methods of seed dispersal include wind, animals, explosions (mechanical ejection), and gravity.
14. How does wind dispersal work?
Answer: Wind dispersal works by blowing lightweight seeds away from the parent plant. Examples include dandelion seeds with their parachute-like structures and maple seeds with their winged design.
15. How do animals help in seed dispersal?
Answer: Animals help in seed dispersal by eating fruits and excreting the seeds elsewhere or by carrying seeds on their fur. Examples include birds eating berries and mammals carrying burrs.
16. What is mechanical ejection (explosions) in seed dispersal?
Answer: Mechanical ejection, or explosions, occurs when seed pods burst open, flinging seeds away from the parent plant. Examples include peas and touch-me-nots.
17. How does gravity aid in seed dispersal?
Answer: Gravity aids in seed dispersal by causing fruits to fall from the parent plant and roll away. Examples include chestnuts and acorns.
18. What adaptations do wind-dispersed seeds have?
Answer: Wind-dispersed seeds often have adaptations such as wings, parachutes, or lightweight structures that allow them to be carried by the wind.
19. What adaptations do animal-dispersed seeds have?
Answer: Animal-dispersed seeds may have adaptations like fleshy fruits to attract animals or hooks and barbs to attach to fur.
20. What is the significance of fruit in seed dispersal?
Answer: Fruits protect seeds and aid in their dispersal by attracting animals with their color, scent, and taste, ensuring seeds are spread to new locations.
21. How do plants ensure successful fertilisation?
Answer: Plants ensure successful fertilisation through mechanisms such as producing large amounts of pollen, attracting specific pollinators, and having structural adaptations that facilitate pollen transfer.
22. What is double fertilisation in flowering plants?
Answer: Double fertilisation is a process in flowering plants where one sperm cell fertilises the egg cell to form a zygote, while the other sperm cell fuses with two polar nuclei to form the triploid endosperm, which provides nourishment to the developing embryo.
23. How does self-pollination differ from cross-pollination in fertilisation?
Answer: Self-pollination occurs when pollen from a flower fertilises ovules within the same flower or plant, while cross-pollination involves pollen transfer between different plants, promoting genetic diversity.
24. What factors affect seed germination?
Answer: Factors affecting seed germination include water availability, temperature, oxygen, and light conditions.
25. How do seeds protect themselves during dispersal?
Answer: Seeds protect themselves during dispersal with tough seed coats, chemical defenses, and structures that aid in dispersal and reduce predation.
26. What is the role of endosperm in seed development?
Answer: The endosperm provides nutrients to the developing embryo within the seed, supporting its growth until it can produce its own food through photosynthesis.
27. What is the significance of seed dormancy?
Answer: Seed dormancy is a survival strategy that prevents seeds from germinating under unfavorable conditions, ensuring they only germinate when conditions are optimal for growth.
28. How do seeds know when to germinate?
Answer: Seeds sense environmental cues such as temperature, moisture, light, and sometimes specific chemical signals, which trigger the germination process.
29. What are some examples of wind-dispersed seeds?
Answer: Examples include dandelions, maples (sycamores), and milkweeds.
30. What are some examples of animal-dispersed seeds?
Answer: Examples include berries eaten by birds, nuts buried by squirrels, and burrs that attach to animal fur.
31. What are some examples of seeds dispersed by mechanical ejection?
Answer: Examples include peas, touch-me-nots, and squirting cucumbers.
32. What are some examples of seeds dispersed by gravity?
Answer: Examples include chestnuts, acorns, and apples.
33. How do plants attract animal pollinators?
Answer: Plants attract animal pollinators with bright colors, sweet scents, nectar rewards, and sometimes specific shapes that accommodate particular pollinators.
34. What is the role of nectar in pollination?
Answer: Nectar attracts pollinators by providing a food reward, encouraging them to visit the flower and facilitate pollen transfer.
35. How do environmental factors influence seed dispersal?
Answer: Environmental factors like wind strength, water currents, animal behavior, and landscape features influence how far and where seeds are dispersed.
36. What is the function of the ovary in seed formation?
Answer: The ovary contains the ovules, which develop into seeds after fertilisation, and later matures into a fruit that encases and protects the seeds.
37. How do seeds ensure they are dispersed far from the parent plant?
Answer: Seeds use various dispersal mechanisms like wind, water, animals, and mechanical ejection to travel away from the parent plant, reducing competition for resources.
38. What are the advantages of cross-pollination?
Answer: Advantages include increased genetic diversity, which can enhance resilience to diseases, environmental changes, and promote healthier plant populations.
39. How do seeds store energy for germination?
Answer: Seeds store energy in the form of starches, fats, and proteins within the endosperm or cotyledons, which provide nourishment during germination.
40. What is the role of the cotyledon in seed germination?
Answer: Cotyledons are seed leaves that store nutrients and provide the first source of energy for the developing seedling during germination.
41. How do fruits aid in seed dispersal?
Answer: Fruits aid in seed dispersal by attracting animals with their color and taste, protecting seeds during development, and sometimes assisting in mechanical ejection or floatation.
42. What adaptations do water-dispersed seeds have?
Answer: Water-dispersed seeds often have buoyant structures or waterproof coatings that allow them to float and travel by water currents to new locations.
43. How do plants ensure seeds land in favorable conditions?
Answer: Plants disperse seeds widely to increase the likelihood that some will land in favorable conditions for germination and growth. Some seeds also have dormancy mechanisms to wait for suitable conditions.
44. What are the main stages of seed development?
Answer: The main stages include fertilisation, zygote formation, embryo development, maturation of the ovule into a seed, and the development of a protective seed coat.
45. How do seed banks contribute to plant conservation?
Answer: Seed banks collect and store seeds from various plant species to preserve genetic diversity, support restoration projects, and protect against plant extinction.
46. What is the significance of seed dispersal in plant evolution?
Answer: Seed dispersal is crucial for plant evolution as it allows species to colonize new areas, adapt to different environments, and maintain genetic diversity through cross-pollination.
47. How do fire-adapted plants disperse seeds?
Answer: Fire-adapted plants often have seeds that require the heat from fires to crack open their seed coats and germinate, ensuring regeneration after a fire.
48. What are the challenges in seed dispersal research?
Answer: Challenges include tracking seed movement, understanding the role of different dispersal agents, and studying the effects of environmental changes on dispersal patterns.
49. How do plants adapt to ensure successful fertilisation?
Answer: Plants adapt through mechanisms like producing attractive flowers, timing flower opening with pollinator activity, and developing specialized structures for efficient pollen transfer.
50. What is the impact of human activities on seed dispersal?
Answer: Human activities such as habitat destruction, pollution, and introduction of invasive species can disrupt natural seed dispersal processes, affecting plant reproduction and ecosystem health.