What is a Fruit?
A seed-bearing structure found in flowering plants or also called angiosperms is known as fruit. It is formed from the ovary present in the seed after flowering in a plant takes place. Angiosperms disseminate seeds with the help of fruits. Many edible fruits are propagated with the help of animals and humans as they help in seed dispersal; fruits are therefore in symbiotic relationship with organisms as they provide nutrition to them and in return get dispersed for new offsprings. Fruits have great agricultural output and some of these have acquired symbolic and cultural significance too.
How is a Fruit Identified?
Fruit is normally associated with the fleshy seed-associated plant structures which are sweet or sour and are usually edible in the raw state. Some of the examples include bananas, apples, grapes, lemons, strawberries and oranges. In botanical terms, fruits are often also associated with other structures namely corn kernels, bean pods, wheat grains and tomatoes. In culinary terms a fruit is defined as a sweet-tasting part of the plant and botanically, a fruit is the ripened carpel or ovary containing the seeds. An important point to be noted is that a nut is a type of fruit and many people might get confused considering it a seed whereas a seed is a ripened ovule.
So, botanically, fruits may include cucumber, squash, eggplant, legumes, like peas, peanuts, brans, chili pepper, sweet paper, etc. Also, a cereal grain like wheat, rice and corn is also a type of fruit known as caryopsis. However, later the fruit wall, being very thin, gets fused to the seed coat and leaves the edible grain which is actually a seed
Fruit Structure
A fruit consists of an important structural component called pericarp.
Pericarp: It is the outer layer which is often edible and is formed from the ovary and it surrounds the seeds. In some species, in addition to this portion, other tissues can form the edible portion as well. The pericarp, further, consists of the following structures:
Epicarp: It is the outermost layer of pericarp.
Mesocarp: It is the middle layer of pericarp.
Endocarp: It is the innermost layer of pericarp.
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Development of a Fruit
The maturation of one or more flowers results in the formation of a fruit and it is the gynoecium of the flower that forms all or some part of the fruit. Let’s discuss the development of a fruit step-wise.
One or more ovules inside the ovary or ovaries are found where egg cells are present in the megagametophyte.
These ovulves become seeds after double fertilization.
The ovules are then fertilized in a process starting with pollination.
Pollination is the movement of the pollen from the stamens to the stigma of the flowers.
After pollination, the pollen leads to the growth of a tube through the stigma into the ovary to the ovule. Further, two sperms are transferred to the megagametophyte from the pollen.
Then, a zygote formation takes place with the unison of one of the sperms with the egg within the megagametophyte.
The second sperm then enters the central cell and forms the endosperm mother cell, thus, completing the double fertilization process.
Later, embryos of the seed are formed via zygote and the endosperm mother cell gives rise to the endosperm which is a nutritive tissue used by the embryo.
As the seeds develop into ovules, the ovary begins to ripen and the pericarp (ovary wall) may become fleshy (such as in berries or drupes) or a hard outer covering (such as in nuts).
The pericarp differentiates into 2 or 4 distinct layers known as the exocarp or epicarp, mesocarp and endocarp.
3 Modes of Fruit Development
Apocarpous fruit development from a single flower with one or more separate carpels; these are the simplest form of fruits.
Syncarpous fruit development from a single gynoecium with two or more carpels that are fused together.
Multiple fruits that rise from multiple flowers.
Different Kinds of Fruits
Simple Fruits
These can be either fleshy or dry and are formed as the result of ripening of a simple or compound ovary in a flower having only one pistil. Dry or simple fruits may be either dehiscent or indehiscent. Some of the fruits belonging to this category include strawberry, wheat, coconut, bean, radish seed, hazelnut, etc.
Simple fruits can be classified further into the following categories:
Drupes: These fruits contain a very hard seed inside themselves, thus, are also known as stone fruits. Some examples are plums and cherries.
Berries: These simple fruits have a juicy interior and have only one seed inside them in the center. Grapes and blueberries are some examples.
Pomes: The kind of simple fruits that grow on trees are known as poems. Papaya and apple are two examples of pomes.
Hesperidium and Pepo: These fruits are somewhat similar to the berries and have juicy centers but have a lot of seeds inside them scattered inside instead of one central seed. Citrus fruits and watermelons are some examples of such fruits.
Aggregate Fruit
These fruits result from single flowers with multiple carpels that are not joined together. It means that each pistil contains one carpel. Each of the pistils forms a fruitlet and collectively, the fruitlets are known as etaerio. Raspberry, blackberry and strawberry are examples of aggregate fruit.
Multiple Fruits
These are the fruits which are formed from a cluster of flowers known as inflorescence. These flowers mature into a single mass and examples include fig, mulberry, pineapple, breadfruit, etc. These types of fruits can also be further divided into two types:
Sorosis: This type of fruit develops from catkin, spikes and spadix type of inflorescences, such as jackfruits, mulberries and pineapples.
Syconus: This type of fruit develops from the hypanthium type of inflorescence.
Benefits and Uses of Fruits
Eating fruits is beneficial for the body as fruits are some of the major sources of essential vitamins and minerals for the body and they are also required for the proper functioning of the body. Citrus fruits are rich in vitamin C which helps prevent scurvy in humans. Fruits are an important part of a healthy diet as they provide nutrients without adding any calories. Research suggests eating fruits can lead to emotional well being and promote a good mood.
Various vitamins like vitamin A, vitamin B6, vitamin C, vitamin E, vitamin K, and folate found in different fruits help in regulating cholesterol levels thus promoting good heart health as well as keeping type-2 diabetes in check by providing the appropriate nutrients to the body. Potassium-rich fruits like bananas, apples, apricots, mangoes and melons help in regulating blood pressure and lower hypertension owing to the vasodilating properties of the mineral found in the fruits.
FAQs on Fruit
1. What is the precise botanical definition of a fruit?
In botany, a fruit is defined as the mature or ripened ovary of a flowering plant (angiosperm), which typically encloses the seed or seeds. Following fertilization, the ovary wall develops into the pericarp, which forms the main body of the fruit. Its primary biological function is to protect the developing seeds and aid in their dispersal.
2. What are the main parts that make up the structure of a typical fruit?
A fruit primarily consists of two main parts: the pericarp and the seeds. The pericarp, or fruit wall, develops from the ovary wall and is further differentiated into three distinct layers:
- Epicarp (or Exocarp): The outermost layer, which forms the skin of the fruit.
- Mesocarp: The middle layer, which is often the fleshy, edible part of the fruit (e.g., in a mango).
- Endocarp: The innermost layer that directly surrounds the seed, which can be hard and stony (as in a plum) or papery (as in an apple).
3. How does a 'true fruit' differ from a 'false fruit' (pseudocarp)?
The key difference lies in the floral parts from which they develop. A true fruit develops exclusively from the ripened ovary of a flower. Mango, plum, and grape are classic examples. In contrast, a false fruit, or pseudocarp, develops from the ovary along with other accessory floral parts like the thalamus, calyx, or receptacle. For example, in an apple, the main edible portion is the fleshy thalamus, not the ovary.
4. What are the three main classifications of fruits? Provide examples for each.
Fruits are broadly classified into three main types based on their development:
- Simple Fruits: These develop from a single, ripened ovary of a single flower. They can be fleshy (like a cherry or tomato) or dry (like a pea pod or wheat grain).
- Aggregate Fruits: These develop from multiple, separate carpels (and thus multiple ovaries) of a single flower. The individual fruitlets merge to form a single unit, like in a raspberry or strawberry.
- Multiple Fruits: These develop from the ovaries of a complete inflorescence (a cluster of flowers). The fruits from all the flowers fuse together into one large fruit, such as a pineapple or a fig.
5. Why are some fruits fleshy while others are dry? Explain the biological purpose.
The difference between fleshy and dry fruits is a direct reflection of their seed dispersal strategy. Fleshy fruits (like berries and drupes) are typically sweet, colourful, and nutritious to attract animals. When an animal eats the fruit, the seeds pass through its digestive tract unharmed and are dispersed far from the parent plant. Dry fruits (like nuts and legumes) often rely on mechanical or environmental forces for dispersal. They may split open (dehiscent) to release seeds, or have structures like wings or hooks to be carried by wind or attach to animal fur.
6. What is parthenocarpy and how does it result in the formation of seedless fruits?
Parthenocarpy is the natural or artificially induced development of a fruit without prior fertilization of ovules. Because fertilization does not occur, no seeds are produced. The ovary is stimulated to grow into a fruit by plant hormones, either naturally produced or externally applied. This process is responsible for producing common seedless varieties of fruits like bananas, pineapples, and some grapes.
7. All fruits develop from an ovary, but not all ovaries develop into fruits. Why does this happen?
The development of an ovary into a fruit is contingent upon successful pollination and fertilization. If pollination fails to occur, or if the pollen is incompatible, fertilization will not happen, and the flower will typically wither and fall off without producing a fruit. Furthermore, even after fertilization, factors like hormonal imbalances, nutrient deficiencies, or environmental stress can lead to the abortion of the young fruit, preventing it from reaching maturity.
8. How does the process of double fertilization in angiosperms specifically lead to the development of a fruit?
Double fertilization is the trigger for fruit development. In this process, one male gamete fuses with the egg cell to form the zygote (which becomes the embryo), while the second male gamete fuses with the central cell to form the primary endosperm nucleus (which becomes the nutritive endosperm). This dual event initiates a cascade of hormonal signals, primarily auxins, which stimulate the ovary walls to enlarge and differentiate into the pericarp, thus transforming the entire ovary into a fruit.
