MEANING OF FRUIT

Subject: 

BIOLOGY

[mediator_tech]

Term:

FIRST TERM

WEEK 5

SUBJECT: BIOLOGY

TOPIC: FRUIT

CONTENT:

1. Structure of fruits

1. Types of fruits
2. Dispersal of fruits
3. Agents of dispersal

SUB-TOPIC I: MEANING OF FRUIT

Fruit is the structure that developed from the matured ovary after fertilization which contains the seed. Some fruits do not develop from fertilized ovary and are called parthenocarpic fruit.

Fruit contains the pericarp (epicarp, mesocarp and endocarp).

Structure of a fruit

Fruits

Simple    Aggregate    Multiple

Dry Dehiscent

Legume or pod

Dry Indehiscent

Achene

Fleshy

Drupe

TYPES OF FRUITS

Fruits can be classified based on their origin or structure. These include:

1. True and false fruit

1. Simple, aggregate and composite (multiple) fruit

1. Fleshy and dry fruit

1. Dehiscent and indehiscent fruits

Simple fruits: Formed from one flower having either a monocarpous or syncarpous pistil.

Aggregate fruits: Formed from one flower having an apocarpous pistil

Multiple fruits: these are fruits formed from many flowers whose ovaries unite together with other parts of the flower after fertilization or one that develops from several flowers inflorescence e.g. pineapple, bread fruit etc.

SIMPLE FRUITS

The simple fruits can be divided into dry and fleshy fruits. A dry fruit is the type of fruit in which the pericarp becomes dry, hard and woody or fibrous when the fruit ripens. Dry fruit may be dehiscent or indehiscent.

DRY DEHISCENT FRUIT: These are fruit with hard and dry pericarp which can split to release their seeds. The dry dehiscent fruit can be divided into five namely: the follicle, legumes, schizocarps, capsule and Siliqua

Follicle: The follicle are fruits that are formed from one carpel and which can split along one side only e.g. kola

Legume: These are fruits that are formed from one carpel that splits along two sides e.g. cowpea, crotolaria and all bean species

Capsule: These are fruits formed from fused carpels and split longitudinally along two or more lines e.g. okra, castor oil and cotton

Schizocarps: These are many seeded fruits which break up into one seeded parts called mericarp e.g. Mimosa pudica (sensitive plant) and Desmodium

Siliqua: A long narrow capsule formed from bicapellary ovary. It has two chambers separated by a false septum or reptum. It dehisces by the sutures e.g. Teconia

DRY INDEHISCENT FRUITS: These are the fruits that do not split to release their seeds. Dry indehiscent fruits are divided into five.

Achene: The fruit has dry pericarp and contain one seed e.g. cashew, nut, sunflower fruit, four O’clock plant, rose and clematis

Caryopsis: the caryopsis is a one-seeded dry indehiscent fruit in which the pericarp becomes fused with testa. Examples are rice, maize and millet

Cypsela: the cypsela is one-seeded dry fruit with hairy pappus and hairy pericarp. Examples are Tridax, Emilia and goat weed.

Nut: A nut is a dry fruit with a very hard or woody or tough pericarp e.g. the hard part of cashew fruit, ground nut, palm nut and cola nut, walnut, and almond.

Samara: A samara has the pericarp extended to form one or more wings e.g. Combretum, Obeche tree and pterocarpous (African rose wood)

FLESHY FRUITS: Fleshy fruits are juicy, succulent and indehiscent. They store large quantities of water and carbohydrate in their tissue. There are six main types of fleshy fruits

namely:

Drupe: This is a true simple fruit with a well-developed pericarp. The epicarp is thin, the mesocarp is fleshy or fibrous and the endocarp is hard and stony. The latter encloses one or more seeds. The hard endocarp with its seed is known as the stone of the fruit e.g. mango, coconut and oil palm fruit.

Berry: A berry is a true simple fruit with a well-developed pericarp. The endocarp is not stony as in drupe. The endocarp is usually a thin membrane covering which is closely attached to fleshy mass made up of the mesocarp and endocarp. Sometimes the whole fruit is eaten. Examples are guava, tomatoes, banana, lemon grape, cucumber date.

Pome: A Pome is a simple false fruit. Examples are apples and pears. In a Pome, the outer covering and the fleshy edible part are formed by the swelling of the receptacle. Only the core is formed from the ovary.

Hesperidium: A Hesperidium is a true simple fruit made up of chambers separated by a sheet of endocarp. The epicarp and mesocarp are fused together in form of a skin (or rind) e.g. orange, lemon, etc.

Differences between fruit and seed

EVALUATION:

1. Define the term fruit.
2. Differentiate between fruit and seed
3. List various kinds of fruits, sort the fruit and classify them
4. What are the three major classes of fruits?

SUB-TOPIC 2: DISPERSAL OF FRUITS AND SEEDS

After the formation and maturation of fruits and seeds, they sometimes fall from the parents to the ground. The number of seeds produced by a single plant is often very large. Most of them perish while some are eaten by animals.

Others may fall on the ground already occupied or unfavourable to the particular plant. When seedlings develop close to the parent plant, they soon become overcrowded. They compete among themselves and the parent plant for light, water, mineral salts and other essential soil constituent so that the strongest seedlings finally survive.

To prevent this, fruits and seeds of most plants are adapted so that they can be scattered far away from the parents, hence fruits and seeds are dispersed.

milkweed; wind dispersal of seeds

ADVANTAGES OF DISPERSAL OF FRUITS AND SEEDS

1. Prevent overcrowding.
2. Reduce degree of unhealthy competition between plants.
3. Introduction of plant species into new environment where they may be better adapted.
4. The dispersal of fruits and seeds also helps to cover barren pieces of land with vegetation.

EVALUATION

1. Why is dispersal necessary in flowering plants?
2. State three advantages of dispersal of fruits and seeds.

SUB-TOPIC 3: AGENTS OF DISPERSAL The common agents that bring about dispersal are;

1. Wind
2. Animal
3. Water
4. Man
5. Explosive mechanisms or explosion

• By Wind: Fruits/seeds carried by the wind or air current must be light, small and have light membranous wings and also having long hairy or thread-like structures which act as parachutes in the air. Wind dispersal is a wasteful process because a great number of seeds may be dropped on sterile or unstable ground or may be carried out into the sea e.g. cotton, poppy, clematics, shorea and augsana, tridax fruit and also Bouganvillea.

• By Animal: Animals like birds, fruit bats and monkeys may be agents of dispersal of fruits and seeds. Many animals feed on the soft succulent fruits but they either discard the strong protected seed of berries, the stony endocarp of drupes and achene or they may swallow them. In the latter case, many of the hardened parts are resistant to enzymes that they pass through the gut without harm and when later dropped can germinate successfully e.g. guava, tomato. Fruits and seeds may be carried externally on an animal’s body by reason of the fact that special hooks or spines which catch in the fur or wool (hairy coats of animals e.g. Desmodium)

• Dispersal by Water: The seed of certain water lilies have air spaces in the pericarp which give the buoyancy required in water. Coconut fruit achieves dispersal of its single seed by floating to new location.

• Dispersal by Man: Dispersal of many fruits and seeds have been aided by the agricultural practices of man e.g. guava, sweet potato and cassava which are native to tropical America now found in all tropical areas in the world.. Seeds of weeds are accidentally transported from one part of the world to another by man’s activities.

• Dispersal by Explosive Mechanism (Self Dispersal): when the fruit wall dries as in the African oil bean, it splits and twists throwing the seed out. The legumes of many bean plants e.g. (Acacia and Ceasalpinia) burst open when ripe. This is by the drying up of the pericarp which causes contraction and splitting e.g. fruit of legumes, pride of Barbados and capsules (fruit of okra-Hibiscus esculentus)

EVALUATION:

1. State four agents of dispersal and explain two of them
2. Why is dispersal necessary in flowering plants?

OBJECTIVE TEST:

1. Which of the following is not a dry indehiscent fruit? (a) legume (b) cypsela (c) samara (d) caryopsis
2. An example of berry is (a) tomato (b) coconut (c) apple (d) pineapple
3. Which of the following is a simple dry dehiscent fruit? (a) berry (b) drupe (c) caryopsis (d) achene
4. A dehiscent fruit formed from several fused carpels with many seeds is classified as (a) an achene (b) a follicle (c) a legume (d) a nut
5. Air spaces are characteristics of seeds or fruits dispersed by (a) birds (b) water (c) wind (d) explosive mechanism (e) man

WEEKEND ASSIGNMENT:

1. Write short notes on true and false fruits
2. Draw and label a longitudinal section of a named fruit, 10 – 12cm long.

SUGGESTED PRACTICAL

1. Arrange the following fruits into either simple or aggregate fruit group: beans, orange, tomato, kola and strawberry
2. Classify orange, mango, pride of Barbados, cashew, apple, pineapple, okra, cotton seed as follows
   • Fleshy fruits
   • Dehiscent fruits
   • False fruits
   • Indehiscent fruits
   • Multiple fruits