Biology

Observe slides containing micrographs of different fruits and seeds. According to
their characteristics:
a. Differentiate fruits.
b. Draw and show a structure of seed as seen on microscope

Below are some examples of fruits:

A fruit is a structure formed from the ovary of a flower, usually after the ovules have been fertilized. It is normally produced only after fertilization of ovules has taken place, but in many plants, largely cultivated varieties such as seedless citrus fruits, grapes, bananas, and cucumbers, fruit matures without fertilization, a process known as parthenocarpy. Ovules within fertilized ovaries develop to produce seeds. In unfertilized varieties, seeds fail to develop, and the ovules remain with their original size.

A fruit consists of two main parts; pericarp (fruit wall) and the seed. The pericarp has three layers: epicarp or exocarp (outermost), mesocarpe (middle) and endocarp (inner).

The fruit can have a dry pericarp or fleshy pericarp. The fruits with fleshy pericarp include: berry and drupe. Drupe is a fleshy fruit with only one seed, E. g. avocado.

Berry is a fleshy fruit having many seeds inside of it. E.g. tomatoes, orange, and pawpaw.

The fruits with dry pericarp include indehiscent fruit or dehiscent fruit. Indehiscent fruits do not open. Seeds remain inside of the fruits. E.g. fruits of coconuts. Dehiscent fruits open and release seeds. They include: dehiscent fruits with one carpel, and those with many carpels. Dehiscent fruits with one carpel include; those which open along one side, e.g. follicle; and those which open along both sides, e.g. legume (beans). Fruits of eucalyptus are examples of dehiscent fruits with many carpels.

The major function of a fruit is the protection of developing seeds. In many plants, the fruit also aids in seed distribution (dispersal).

Fruits  are  eaten  raw  or cooked, dried, canned, or preserved. Carbohydrates, including starches and sugars constitute the principal nutritional material of fruits. Citrus fruits, tomatoes, and strawberries are primary sources of vitamin C, and most fruits contain considerable quantities of vitamin A and vitamin B. In general, fruits contain little protein or fat. Exceptions are avocados, nuts, and olives, which contain large quantities of fat, and grains and legumes, which contain considerable protein.

A seed is an embryonicplant enclosed in a protective outer covering. The formation of the seed is part of the process of reproduction in seed plants, the spermatophytes, including the gymnosperm and angiosperm plants. Seeds are the product of the ripened ovule, after fertilization by pollen and some growth within the mother plant. The embryo is developed from the zygote and the seed coat from the integuments of the ovule.

The main components of the embryo are: seed made up of a seed coat (testa), one or two cotyledons and an embryonic axis. The embryonic axis is made up of a plumule, an epicotyl, a hypocotyl and a radical. A seed which has one seed-leaf is described as monocotyledonous and one which has two, as dicotyledonous. Maize is monocotyledonous seed while bean is a dicotyledonous seed.

– The cotyledons: the seed leaves attached to the embryonic axis. There may be one (Monocotyledons), or two (Dicotyledons). The cotyledons are also the source of nutrients in the non-endospermic dicotyledons, in this case, they replace the endosperm, and they are thick and leathery. In endospermic seeds, the cotyledons are thin and papery.

– The epicotyl: the embryonic axis above the point of attachment of the cotyledon(s)

– The plumule: It is located at the tip of the epicotyl and has a feathery appearance due to the presence of young leaf primordial at the apex. It will become the shoot upon germination.

– The hypocotyl: the embryonic axis below the point of attachment of the cotyledon(s) connecting the epicotyl and the radicle, being the stem-root transition zone.

– The radicle: the basal tip of the hypocotyl and it grows into the primary root.

Monocotyledonous plants have two additional structures in the form of sheaths. The plumule is covered with a coleoptile that forms the first leaf while the radicle is covered with a coleorhiza that connects to the primary root and adventitious roots form from the sides. Here the hypocotyl is a rudimentary axis between radicle and plumule.

Self-Assessment 17.4
1. Describe the structure of a drupe
2. Differentiate between a drupe and a berry
3. What would happen to the fruit if ovules in the flower did not develop?
4. Compare the typical structure of seeds that are dispersed by animals to those dispersed by wind and water.

Use books and internet and to answer to the following questions:
1. Suggest the ways of fruits and seeds dispersal.
2. Explain adaptation of fruits dispersed by animals.

Dispersal of fruits and seeds is the scattering of fruits and seeds from their mother plants. They are four methods of seeds and fruits dispersal such as: (1) Dispersal by Wind (2) Dispersal by Water (3) Dispersal by Animals and (4) Mechanical Dispersal. Seeds dispersed by wind or water are typically lightweight, allowing them to be carried in air or to float on the surface of water. The wind carries also small seeds that have wing-like structure. Seeds dispersed by animals are typically contained in sweet and nutritious flesh fruits. They can be carried externally on their feet, fur, feathers, or beaks. Those seeds with hooks or sticky substances rely on the chance that they will attach themselves to a passing animal. Other seeds are eaten by animals and passed out in the faeces. These seeds will germinate where the faeces will be deposited.

With mechanical dispersal: all dehiscent fruits scatter the seeds when they burst. This dehiscence is accompanied by the expression of great force in many fruits so that seeds are jerked at a considerable distance away from the mother plant. Such fruits are called explosive fruits.

The dispersal of seeds is important for the survival of the plant species because:

–– It minimises overcrowding of plants growing around the parent plant that
could then result in too much competition for nutrients and light;
–– It allows the plant species to colonise new habitats which can offer suitable
conditions.

Self-assessment 17.5
1. Why is it adaptive for some seeds to remain dormant before they germinate?
2. The seeds of a bishop pine germinate only after they have undergone a forest fire. Evaluate the significance of this structural adaptation.
3. Evaluate the importance of seed dispersal.

End of unit assessment 17
1. Answer by true or false
a. Mosses have life cycle that depends on water for reproduction.
b. In ferns, the gametophyte depends on sporophyte.
c. In mosses, the sporophyte dominates over the gametophyte.
d. Seeds that are dispersed by animals are not contained in a flesh-sweet
tissue.
e. During pollination, pollen grains move from stigma to anthers.
2. Chose the letter that best answers the question or complete the statement.
a. Which of the following is not part of a flower?
i. Stamens
ii. Petals
iii. Carpels
iv. Stem
v. Sepals
b. Which is the structure of a flower that includes all parts listed below?
i. Stigma
ii. Carpel
iii. Ovary
iv. Style
v. Ovule

c. The thickened ovary wall of a plant may join with other parts of the flower to
become the
i. Cotyledon
ii. Fruit
iii. Endosperm
iv. Seed
d. In angiosperms, the structures that produce the male gametophyte are called
the
i. Pollen tubes
ii. Stigma
iii. Anthers
iv. Sepals
e. The small and multicellular structures by which liverworts reproduce
asexually are
i. Archegonia
ii. Gemmae
iii. Protonema
iv. Rhizoids
f. In angiosperms, the mature seed is surrounded by a
i. Flower
ii. Fruit
iii. Cotyledon
iv. Cone
g. The leaves of ferns are called
i. Spores
ii. Fronds
iii. Sori
iv. Rhizomes
h. The most recognizable stage of a moss is the
i. Gametophyte
ii. Archegonium
iii. Protonema
iv. Sporophyte
3. Which are more likely to be dispersed by animals- the seeds of angiosperms or the spores of a fern? Explain your answer.
4. Pollination is a process that occurs only in seed plants. What is the process in
seedless plants is that is equivalent to pollination?

5. What is the dominant stage of the ferns life cycle? Explain the relationship
between gametophyte and sporophyte phases of the fern
6. Why is water essential in the life cycle of a bryophyte?
7. What is the characteristic responsible for the small size of bryophytes? Explain.
8. Briefly explain why a seed may remain dormant even when the environmental
conditions are favorable for germination.
9. Describe the relationship between the gametophyte and sporophyte in
mosses.
10. During the lifecycle of a moss, what are the environmental conditions
necessary for fertilization to occur?
11. Describe the dominant stage in the lifecycle of a fern.
12. Propose a hypothesis to explain why angiosperms have become the dominant
type of plant on the earth.
13. Moss plants are small. Ferns can grow as tall as small tree. Explain why. How
does your answer illustrate a major characteristic of the plant kingdom?
14. Study the structure of the seed bellow

a. Name the parts A, B and C
b. What is the importance of the part C for a growing seedling?
15. Many flowers have bright patterns of coloration that directly surround the
reproductive structures. Evaluate the importance of those bright-colored
patterns to plants.
16. What is the function of endosperm?
17. Some plants form flowers that produce stamens but no carpels. Could fruit
form on one of these flowers? Explain your answer.
18. Distinguish between pollination and fertilization.

19. Give names corresponding to the following to the letters: from A to J. Explain
the function of the parts represented by: B, G, and E.

20. Explain why the relationship between bees and flowers is described as
mutually beneficial.
21. What is the main advantage of cross-pollination?
22. Why are the stamens of wind-pollinated plants and insect-pollinated plants
different?
23. Differentiate wind-pollinated flowers from insect-pollinated flowers.
24. Give one example of a plant that uses each of the following dispersal
mechanism:
a. An explosive device which works by being inflated with water.
b. A winged seed lifted by air currents
c. A buoyant seed carried by sea currents
d. A gluey substance which sticks the seed to an animal.