presentation on biology for grade 6 “Distribution of fruits and seeds”

Oak fruits are spread by water

20.2.8. Distribution of fruits and seeds

After seed formation, either the entire fruit or the seed (or seed) it contains is separated from the parent sporophyte.
If the pericarp (wall of the fruit) becomes hard and dry, the fruit is called dry, but if it becomes fleshy, then the fruit is called juicy. A dry fruit may be dehiscent or indehiscent, depending on whether the release of the seeds is associated with rupture of its wall or not. Dry fruits can also split into several single-seeded segments; such fruits are called schizocarpous. The further the seeds are dispersed, the less likely there is competition from the parent plant. This also gives them a greater chance of colonizing new territory, leading to an increase in overall population size over time. However, there is a danger that the seed, being carried too far from the parent plant, will not find a suitable place for germination.

There are three main external factors that disperse seeds - wind, animals and water. In addition, there are mechanisms of autochory, often associated with the explosive release of seeds from the fruit. Examples of all these methods of seed dispersal are presented in Fig. 20.28.

Animal seed dispersal is generally more reliable because animals tend to visit fertile areas suitable for seed germination. The fruits, equipped with spines or hooks, cling to the skin or fur of passing animals and can be carried some distance before falling off or being torn off. Attachments develop from different parts of the fruit or surrounding structures. Examples are the fruits of the tenacious bedstraw ( Galium aparine

), gravilate (
Geum
), burdock (
Arctium
), carrot (
Daucus
), buttercup (
Ranunculus
), string (
Bidens
), agrimony (
Agrimonia
). Gravilat has hooks on the post. In burdock, a cluster of small fruits is surrounded by hooked involucre leaves (modified leaves) forming a single structure; In addition, there are small, hard hairs that penetrate the skin, causing irritation and scratching, as a result of which the fruits fall off. In bedstraw, carrots and buttercups, the pericarp is covered with projections (attachments). In the series, the fruit is equipped with a fly, like a dandelion, but with strong thorns. The receptacle of the agrimony is covered with hard, curved spines.

Rice. 20.28. Different types of fruits and seeds and how they are distributed. Bedstraw (Galium aparine) and agrimony

Bedstraw fruit with numerous hooks developing from the pericarp. Micrograph taken using a scanning electron microscope.

Examples of juicy fruits are plum fruits ( Prunus

), blackberry (
Rubus
), tomato (
Lycopersicum
), apple (
Malus
), strawberry (
Fragaria
). The fleshy parts of these fruits serve as food for animals, including birds. When ripe, they usually acquire bright colors and aroma that attract animals. The animal eats and digests the fruit, but the seeds, resistant to digestive enzymes, pass unharmed through its intestines and are excreted, often landing on fertile soil. Nutrients contained in excrement can increase the fertility of the soil around the seed.

The plum is an example of a fruit called a drupe; its pericarp consists of three layers: the exocarp (protective skin), the succulent mesocarp and the internal stony endocarp (“pits”). These layers protect the seed, preventing it from being digested. Other examples of drupes include peach, cherry and almond fruits (also belonging to the genus Prunus

), elderberry (
Sambucus
) and coconut palm (
Cocos nucifera
; fruit with a fibrous mesocarp). Almonds that go on sale are usually cleaned of the subcarp and mesocarp.

Rice. 20.28. Different types of fruits and seeds and how they are distributed. Plum (longitudinal section)

Rice.
20.28. Different types of fruits and seeds and how they are distributed. A blackberry berry in a longitudinal section is a collection of drupes formed from one flower. The tomato fruit, formed as a result of the fusion of two, three or four carpels, belongs to the type of berry-shaped

.
It is similar to a drupe, but its endocarp is fleshy rather than stony. The berry-like fruits also include the fruits of black currant and gooseberry ( Ribes spp.
), pumpkin (
Cucurbita
), orange and lemon (
Citrus spp.
), banana (
Musa
), grape (
Vitis
), date (
Phoenix dactylifera
; contains one woody seed).

Rice.
20.28. Different types of fruits and seeds and how they are distributed. Tomato (longitudinal section) Sometimes the receptacle swells, becomes fleshy and itself resembles a fruit. Such fruits are called false. Examples include apple and strawberry fruits.

The false fruit of the apple tree is a type of apple, or pumpkin. In fruits of this type, the pulp is formed from a hollow receptacle surrounding the enclosed carpels. The pericarp of the true fruit develops into a “core” containing the seeds. Other examples include the pear ( Pyrus

) and hawthorn (
Crataegus
)

Rice.
20.28. Different types of fruits and seeds and how they are distributed. Apple (longitudinal section) Strawberries have small green fruits called achenes and located on an overgrown receptacle; each achene contains one seed.

Rice. 20.28. Different types of fruits and seeds and how they are distributed. Strawberry (longitudinal section)

Nut-shaped

fruits, for example, oak (
Quercus
), beech (
Fagus
), chestnut (
Casta nea
), relatively large dry fruits that do not split and do not throw out seeds. Nut-shaped fruits are distributed entirely, often with the help of stocking animals, especially rodents such as squirrels. The picture shows an oak fruit called an acorn.

Rice.
20.28. Different types of fruits and seeds and how they are distributed. The fruit of the oak tree is an acorn. Many wind-dispersed plants have special adaptations. These include volatiles, which are supplied, for example, with fireweed seeds ( Epilobium

), willow (
Salix
), cotton (
Gossypium hirsutum
), dandelion (
Taraxacum
), clematis (
Clematis
), and lionfish, such as pine (gymnosperm), elm (
Ulmus
), ash (
Fraxinus
), maple (
Acer
), hornbeam (
Carpinus
).

Who sows the oaks?

What kind of adaptations do plants to continue their species and disperse seeds ?
There are parachutes, like those of dandelions, and tenacious spines (they stick to a person’s clothing or to the fur of an animal - and travel until they fall into the ground), like those of a string, a plantain. Light seeds of birch, pine, and spruce are carried far away by the wind over the snow crust. Insects and animals (elephants, wild pigs, for example, are perhaps the only distributors of crushed fruits with seeds of the Rafflesia Arnoldi plant, which has the largest flower in the world. And this amazing plant grows on some islands in Southeast Asia) also distribute seeds many plants.

Many fruits are dispersed by birds. But what is it like for the oak tree? Round, smooth, large acorns are too tough for birds, and they are not able to cling to anything, and the wind will not carry them away.

However, young trees can often be found among pine plantings, where mature oaks are nowhere to be seen. It turns out that the oak tree has sowers.

Jays , making supplies for the winter, carry acorns over long distances, hiding them in moss or fallen pine needles. For jays living in the European part of Russia, Ukraine, and Belarus, the main food is acorns. The jay makes significant reserves of them for the winter, up to 4 kg. And then they forget about their pantries - can you really remember them all? So oak trees grow in the most unexpected places.

Source

Oak fruits are spread by water

In plants with single-seeded dry fruits (acorn, nut, achene, grain), the fruits themselves are scattered along with the seed. The seed coat of such seeds is poorly developed, because The protection function is performed by the pericarp. Such fruits are often distributed by animals that feed on them and store them (chipmunks, squirrels, mice). The seeds of juicy fruits are distributed by animals that eat them. Such seeds should retain the ability to germinate after passing through the animal’s digestive tract (some even improve their germination rate). Therefore, they have a dense seed coat (for berries) or a stony layer of the pericarp - a stone.

Some seeds are carried by insects. For example, ants drag grass seeds with succulent appendages-outgrowths (celandine, hoofed grass, violet). Therefore, thickets of these plants can also indicate ant trails.

Cross pollination of different plants

One of the ways plants reproduce in forest conditions is cross-pollination of different plants . The early flowering of hazel, alder, aspen, willow, (more: Early flowering trees and shrubs) and oak forest grasses, the flowering of plants with white flowers, when the oak forest trees become leafy and the forest becomes dark - all these are examples of plants adapting to cross-pollination.

alder blossom

The flowering of undergrowth trees has the same characteristics - wild apple and pear trees, mountain ash, viburnum, elderberry and many other trees also have white flowers, and this helps insects find them in the darkness of the forest.

Elderberry color

Methods of distribution of fruits and seeds

After seed formation, either the entire fruit or the seed (or seed) it contains is separated from the parent plant. The longer the seeds are dispersed, the less likely there is competition from the parent plant. This also gives them a greater chance of colonizing new territory, leading to an increase in overall population size over time. However, there is a danger that the seed, being carried too far from the parent plant, will not find a suitable place for germination.

Care tips: watering, fertilizing, pruning

Caring for oak is not particularly difficult:

1. The regularity of watering is determined by the dryness of summer or spring. If the drought period is long, then a bucket of water is poured per square meter of crown projection. Watering is especially important for young plants in extreme heat.
2. Feed the tree twice. At the beginning of spring, a kilogram of mullein, ten grams of urea, and twenty grams of ammonium nitrate are diluted in ten liters of water and the area of ​​the root circle is watered. In September, no more than twenty grams of nitrophoska are added.
3. Weeds are constantly removed from around the tree and the soil is loosened to a depth of twenty-five centimeters.
4. Crown pruning is carried out in autumn or early spring, during the dormant period, removing dried branches. In this case, the air temperature should not be lower than minus five degrees, otherwise the tree will freeze. The procedure is necessary to clean the trunk from top shoots. The tree crown is also formed by pruning. In the fall, 2-3 axial branches in the center of the crown are cut to a standard, shortening the lateral ones. On thick branches, cuts are treated with garden varnish or natural paint. In spring, the oak tree will be pleased with its spherical crown, and the height of the tree will decrease. If it is necessary to stop the growth of the giant in height, then the apical bud is cut off, pinching the central shoot. Thin shoots six centimeters in diameter must be removed from red oak trees.

Caring for oak is simple and does not require any material or time costs.