Biology SS2 Second Term
Week: 4
Topic: The Fruit
Introduction
A fruit is the ripened ovary or ovaries of a flowering plant, together with accessory parts consolidated with it, containing the seeds and occurring in a wide variety of forms and to some extent assists in the dissemination of the seeds.
Typically a fruit start to develop after that an ovule is fertilized as a result of the process of pollination, the ovary begins to enlarge. The petals of the flower drop and the ovule develops into a seed.
The ovary, together with accessory parts of the flower or other organs comes to form a structure surrounding the seed, which is the fruit. Fruit development continues until the seeds have matured.
Structure of a Fruit
The fruit is a complex structure composed of many different parts. Some of the more common terms used for describing a fruit are:
Pericarp: The fruit wall, often composed of three layers: epicarp, mesocarp, and endocarp.
Epicarp or exocarp (also called ectocarp): The outermost layer of the pericarp (the skin) .
Mesocarp: The middle layer of the pericarp (the fleshy pulp).
Endocarp: The innermost layer of the pericarp (the stone or pit).
Mericarp: A portion of fruit that seemingly matured as a separate fruit.
Seed: Mature ovules composed of a seed coat, endosperm, and embryo.
Placenta: Region of attachment of seeds on inner fruit wall.
A fruit normally consists of the following parts:
- The fruit wall or pericarp
- The seed or seeds inside the fruit
- The remains of the style or scar showing point of attachment of the style
- The fruit stalk or scar showing point of attachment of the fruit to the plants
Differences between a fruit and seed
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Fruit |
Seed |
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1. |
Fruit develops from an ovary and so contains seed(s) |
Seed develops from an ovule and so contains an embryo |
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2. |
It has fruit stalk or a scar (due to receptacle) |
It has a scar (hilum) formed by attachment of funicle |
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3. |
It bears remains of style or scar left by it |
It does not bear remains of style |
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4. |
It has no micropyle |
It has micropyle |
Classification of Fruits
Fruits are classified into different groups depending on their origin and structure. The following are the common ways of classifying fruits:
- True and false fruits
- Simple, aggregate and composite (multiple) fruits
- Fleshy and dry fruits
- Dehiscent and indehiscent fruits
True and False Fruits
- False fruit: A fruit derived from the ovary and its contents as well as other parts of the flower; it is usually derived from an inferior (inserted below other floral parts) ovary. Also known as inferior fruit. E.g. Apple, pineapple, cashew, etc.
- True fruit: A fruit that is derived from only the ovary, usually derived from a superior (inserted above the other floral parts) ovary. Also known as superior fruit. E.g. Cowpea, mango, orange, etc.
Simple, Aggregate and Composite (Multiple) Fruits
- Simple fruits: One fruit that has developed from one single flower. Most fruits are simple fruits, for example apples, pears, tomatoes, peaches, and cherries.
- Aggregate fruits: One flower that produces many tiny fruits clustered tightly together, like raspberries, blackberries and strawberries. (NOTE: in strawberries, the fruits are actually the seed-like things on the outside of the flesh, the flesh itself is not the ovary but swollen receptacle tissue).
- Multiple fruits: Fruits from many different flowers which develop closely together to form one bigger fruit, like pineapples, breadfruit and mulberries.
Fleshy and Dry Fruits
Fleshy Fruit
A fleshy fruit is the type of fruit in which the whole pericarp or at least one of its layers is thick, soft and fleshy (succulent) especially when it is ripe. Fleshy Fruits can be subdivided again into those formed from a single flower and those formed from a group of flowers. They can have one seed or several seeds in. Practically, all fleshy fruits are indehiscent.
Fleshy Fruits formed from a single flower are classified as: Berry, Drupe, and Pome.
- Berry: A Berry is a single soft and fleshy fruit without a stone, usually containing a number of seeds. Fruits of this type are: Banana (Musa), Coffee (Coffea arabica), Pepper (Capsicum), Tomato (Lycopersicon esculentus), orange, melon, guava and pawpaw.
Tomato Fruit- A berry
- Drupe: A Drupe is a single fleshy fruit with a hard stone which contains the single seed. In drupe, the epicarp is thin, the mesocarp may be fibrous, e.g. coconut (Cocos nucifera) and oil palm nut or fleshy, e.g. mango while the endocarp is hard and stony. Other fruits of this type are: Olive (Olea europaea), Peach (Prunus persica).
Similarities between a Drupe and a Berry
- Both have fleshy or succulent mesocarp
- Both have thin epicarp
- Both have seed(s)
Differences between a Berry and a Drupe
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Berry e.g. Tomato |
Drupe e.g. Mango |
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1. |
Berry has many seeds |
Drupe has only one seed |
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2. |
Mesocarp and endocarp are fused |
Mesocarp and endocarp are not fused |
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3. |
Mesocarp and endocarp fuse to form soft pulp |
Drupe has hard endocarp |
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4. |
Endocarp is edible |
Endocarp is not edible |
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5. |
Mesocarp is edible |
Mesocarp may or may not be edible |
Pome: A Pome is a fleshy fruit with a thin skin, not formed from the ovary but from another part of the plant. These are simple false fruit. The seeds are contained in chambers in the centre of the fruit. an Other fruits of this type are: Apple (Malus domestica), Pear (Pyrus communis), Quince (Cydonia oblonga).
Fleshy Fruits which grow from a group of flowers are classified as: Sorosis, Synconium, Coenocarpium.
There are a few fruits formed from a group of flowers (inflorescence) rather than just one, but which form only one fruit. These are Sorosis, as in the Mulberry (Morus), Syngonium, as in the Fig (Ficus), and Coenocarpium, as in the Pineapple (Ananas).
