1) Fill out the diagram.
2) Complete the laboratory work “Structure of seeds of dicotyledonous plants” (see p. 9 of the textbook). Label the parts of a bean seed in the picture.
3) Complete the laboratory work “Structure of wheat grain” (see p. 10 of the textbook). Label the parts of a wheat grain in the picture.
4) Fill out the table "Comparison of seeds of dicotyledonous and monocotyledonous plants."
6) Study the structure of an apple, pumpkin or sunflower seed. Sketch the structure of one of the seeds. Analyze the structure of the seed you studied and draw a conclusion.
Conclusion: A pumpkin seed consists of an embryo, 2 cotyledons, and a seed coat. There is no endosperm. The function of storing substances is performed by the cotyledons. The type of pumpkin seeds is dicotyledonous seeds without endosperm.
7) Explain why seed plants are the most common in nature.
Answer: Seed plants have the most developed adaptations for reproduction - double fertilization, which does not require water, protection of the embryo by the seed coat, and the presence of nutrients for the embryo contained in the cotyledons or endosperm.
13. STRUCTURE OF SEEDS OF FRUIT PLANTS Purpose of the lesson. Familiarize yourself with the structure of seeds of the main pome and stone fruit species. To study the morphological characteristics of seeds of the main pomaceous, stone fruit and nut-bearing species and, based on their distinctive features, learn to distinguish between seeds of different breeds, types and forms.
In fruit growing, the concept of seeds has a biological and production meaning, reflecting their main function - the ability to germinate. Therefore, a seed is understood as an embryo surrounded by shells of various origins: the seed coat (in pome crops), the seed coat and endocarp (in most stone fruit and partially nut crops), the seed coat and pericarp (some nut and berry crops). Often seeds are called drupes, nuts, etc.
In fruit plants, after double fertilization is completed, a seed is formed from the ovule, and the outer integuments of the ovule (or integuments) turn into the seed coat. The nucellus cells are used by the growing embryo or, less commonly, transformed into nutritious tissue - perisperm. In most fruit and berry plants, the endosperm and nucellus cells are used to form the embryo, and reserve plastic substances are localized in the cotyledons of the embryo (Fig. 18).
Figure 18. Anatomical structure of an apple seed
1- root of the embryo; 2 – primary kidney; 3 – seed coat; 4 – cotyledons; 5 - endosperm; 6 – chalaza; 7 – vascular-fibrous bundle; 8 - micropyle
Depending on the location of accumulation of plastic substances, the following types of seeds are distinguished.
Seeds with endosperm. Reserve substances accumulate in endosperm tissues, cotyledons are poorly developed (persimmon, grapes, edible honeysuckle, viburnum). In most deciduous fruit plants, the endosperm is preserved in the form of a thin film of obliterated cells adjacent to the embryo. In apple seeds, this endosperm film partially functions as a regulator of water absorption by the embryo.
Seeds without endosperm. Reserves of plastic substances are concentrated in the cotyledons. The seeds of most fruit and berry plants are protein-free; at the beginning of full seed maturation they do not have perisperm, and the endosperm is preserved in the form of a thin film of non-living, often half-destroyed cells. Almost the entire volume of the seed is filled by the cotyledons of the embryo, pushing the endosperm cells towards the skin. The endosperm is a nutritious tissue in the initial period of embryo development, then its functions are performed by the cotyledons.
The seed consists of an embryo surrounded by a film of endosperm and then a seed coat. The peel has a complex anatomical structure; it protects the embryo from the penetration of microorganisms, regulates the absorption of water and mineral nutrients, and in certain fruit crops it can influence the duration and depth of dormancy of the embryo. In pome-bearing plants, the seed coat is pigmented. In stone fruit and nut-bearing species, the functions of the peel are partially performed by the seed - the endocarp of the fruit, therefore their seed coat is thin and fits tightly around the embryo. The seed coat often fuses with the endosperm and is separated from the embryo along with it.
The formed embryo includes well-developed large cotyledons, between which there is a rudimentary bud (plumule) with an embryonic stalk - the supracotyl (epicotyl) and the subcotyledon (hypocotyl) with the embryonic root. A shoot subsequently develops from the plumule, a main root from the embryonic root, and a root collar from the hypocotyl. After opening, the cotyledons turn green and assimilate instead of leaves, and after the formation of true leaves they fall off.
The seeds of pome crops are divided into the following parts based on their external structure:
Base, or spout, seed- usually the pointed and elongated part of the seed. The fruit scar is clearly visible on it - the place where the seed is attached to the achene, along which the vascular-fibrous bundle passes. When the seed ripens, the achene comes off, but a trace (scar) remains.
Top of the seed– the part opposite the base. Usually the apex is wider, often rounded, and blunt.
Micropyle, or spermatic opening,- a hole in the peel located next to the rumen. Previously, this hole served for the penetration of the pollen tube and was called the pollen duct. Water penetrates into the seed through the micropylar opening, and the tip of the embryonic root is located near it.
Ventral or ventral side(from the Latin ventrum - belly) - part of the seed along which the vascular-fibrous bundle from the seed stalk (ventral suture of the seed) passes in the seed coat. A single vascular bundle from the base of the seed, from the hilum, goes along the suture to the apex of the seed on the ventral side opposite the micropyle. At the top of the seed, under the skin, the strand of the vascular bundle is most developed, and usually in this place the growth of the seed coat is observed. This part of the seed is called chalaza, and the overgrown part of the peel - chalazic projection.
Dorsal, or dorsal side(from the Latin dorsum - back) - the part of the seed opposite the ventral side. The dorsal part of the seed is usually more abruptly curved; a vascular bundle also runs along it from the chalaza to the base (not externally noticeable). It ends near the micropylar opening, on the side opposite to the scar. Thus, the vascular bundle goes around almost the entire seed (it does not penetrate the embryo), and with its help the seed receives nutrients from the mother plant. Plastic substances from the mother plant enter through the vascular bundle into the nutrient layer (endosperm) and internal integuments of the seed coat and are consumed from them by the embryo.
Figure 19. Morphological structure of fruit crop seeds:
a – apple trees; b, c – plums; g – cherries; 1 – base; 2 – top; 3 – chalazal protrusion; 4 – ventral side; 5 – dorsal side; 6 – vascular-fibrous bundle; 7 – sides of the bone; 8 – bone ribs; 9 – seed core; 10 – endocarp; 11 – groove; 12 - roller
Seeds and nuts have the following parts (Fig. 19).
Base – part of a seed or nut adjacent to the stalk and connected to it during the formation of the fruit by a conductive bundle. The junction of the seed or nut with the bunch and stalk is clearly visible and for certain crops (hazelnuts, chestnuts, almonds) is a clear distinguishing feature.
Vertex– part of the stone or nut opposite the base. In some species (plum, cherry plum, almond) it is narrowed and pointed, in others it is somewhat blunt and has a gap (real pistachio). In hazelnuts, chestnuts, walnuts, cherries, and others, the top differs little from the base.
Abdominal side- part of the stone through which the vascular bundle passes from the stalk to the apex. In the upper part of the seed, during the formation of the fruit, the bundle is connected from the inside with the help of an achene with the vascular bundle of the seed. Morphologically, the ventral side of nut crops (except pistachio and almond) is almost no different from the ventral side. In almonds and stone fruits it has one pronounced longitudinal rib, often delimited from the sides of the stone by noticeable longitudinal grooves. In the absence of a pronounced rib, this part of the bone is blunt and keeled.
Dorsal side- part of the bone opposite the abdominal one. In nut crops, the ventral side is morphologically almost identical to the dorsal side.
Sides– parts of a seed or nut located between the ventral and dorsal sides. In some nut crops (hazel, pecan, chestnut), the sides are not pronounced and are difficult to distinguish, but in almonds and stone fruits they are often covered with a relief pattern (endocarp sculpture).
The main morphological characteristics that allow us to determine the breed and species of seeds of pome crops are the following.
The structure of the base of the seed. Relatively smooth or straight (various types of apple and pear trees); slightly curved towards the ventral side (Siberian apple tree); curved in the form of a comma (rowanberry); elongated in the form of a beak (irga rotundifolia).
Figure 20. Distinctive features of pome crop seeds:
A – shape of the base of the seed: 1 – in the form of a comma; 2 – in the form of a beak; 3 – relatively straight; 4 – slightly curved; B – seed shape: 1 – regular; 2 – partially compressed; 3 – bilaterally compressed; 4 - plano-convex
Seed shape(Fig. 20) a regular (oval) shape is formed when the seeds are located freely and do not put pressure on each other during development in the seed chamber - 5-10 seeds per fruit (typical for cultivated varieties of apple trees); a flat-convex shape is formed when two seeds develop in the seed chamber with one side in full contact - 10 seeds per fruit (various types of pear, plum-leaved apple tree, round-leaved serviceberry); a partially compressed form is formed when the contact surface of the seeds in the seed chamber is small - 15-20 seeds per fruit (forest apple, Siberian apple, mountain ash); a bilaterally (trilaterally) compressed form is formed when a large number of seeds develop in the seed chamber - 60-80 per fruit (common quince).
Seed coloring. Reddish-brown (common pear, rowan); chestnut with a whitish coating (common quince); dark chestnut (irga rotundifolia); brown-brown (domestic apple, forest, plum-leaved); light brown (Siberian apple tree); from gray to black (Ussuri pear).
By seed size(for seeds of pome crops, their number per unit of mass, 1 g, is used) domestic apple tree - 20-30; forest apple tree – 30-50; plum-leaved apple tree – 50-75; Siberian apple tree – 170-200; common pear, Ussuri pear – 25-30; forest pear – 45-50; common quince – 25-40; irga roundifolia – 200-215; ordinary rowan – 240-260.
The seeds of stone fruit crops differ from each other according to the following morphological characteristics.
According to the structure of the ventral side of the stone: there is a groove on the ventral side (plum, damson, sloe, cherry plum, peach); on the ventral side there is a convex seam, or ridge (types of cherry, sweet cherry, apricot, almond, bird cherry).
According to the nature of the surface of the pit: smooth (types of cherries, sweet cherries, cherry plums, virgin bird cherry); rough (apricot); pitted (plum, sloe, damson); wrinkled (peach, bird cherry); porous (almond).
According to the shape of the seeds: round (types of cherries, sweet cherries, sloe, bird cherry); oval (cherry plum, damson, apricot, peach); elongated (plum, almonds).
By seed size: small, less than 10 mm long (types of cherries, sweet cherries, sloe, bird cherry); medium, 10-20 mm long (plum, damson, cherry plum); large, more than 20 mm long (apricot, peach, almond).
Tasks. 1) Divide the seed mixture into three groups: pome, stone fruit and nut-bearing species.
2) Draw and label in the drawing: a) for an apple seed - the top and base, the fruit scar, the micropyle and the chalazal protrusion (or spot), the seed suture; find the dorsal and ventral sides; mark the hypocotyl pole, paying attention to the spout of the seed; b) find and mark the top and base of the pit and nuts, the place of entry of the vascular bundle and its passage, mark the dorsal and ventral sides of the plum.
3) Provide a brief description of the types and forms of seeds, indicating their characteristic features, size and shape. Record the obtained data in tables 9 and 10.
9. Structure of seeds of pome crops
10. Structure of stone fruit seeds
| Species name | Bone | Side structure |
|||
| size | surface | form | dorsal | abdominal |
|
Materials and equipment. Dry seeds, drupes and nuts and pre-soaked (2-3 days) apple seeds. Collections and diagrams of the structure of seeds of fruit and nut plants. A set of reference samples of seeds of pome, stone fruit and nut-bearing species. Sets of seeds in bags for their analysis and identification. Tables with pictures and morphological characteristics of seeds. Schemes of the structure of seeds of pome, stone fruit and nut-bearing plants. Magnifying glasses, collapsible boards, spatulas, lancets.
Control questions. 1. Describe the structure of seeds of pome crops. 2. What is the structure of stone fruit seeds? 3. List the distinctive features of stone fruit seeds.
To describe a pumpkin, first of all, you should start with its fascinating history. It is known that pumpkin has been cultivated by Russians since ancient times, but the exact homeland of pumpkin has not yet been established. Pumpkin has gained wide popularity due to its high yield. Pumpkin fruits can reach gigantic sizes. Pumpkin is not only productive, but also very useful. Its pulp contains salts of potassium, calcium, magnesium, sodium, phosphorus, iron and other elements. It is rich in carbohydrates (starch, various sugars), fiber and pectin substances, which promote the absorption of food, improve metabolism and remove toxins from the body. Pumpkin contains vitamins C, A, B1; B2, PP. Pumpkin seeds contain up to 46% fat (oil is extracted from them). For a long time they have been used in folk medicine as an anthelmintic.
Modern medicine recommends the use of pumpkin plant seeds in the treatment of prostatitis. Pumpkin is indispensable in dietary nutrition, for atherosclerosis, diseases of the heart, intestines, kidneys, liver and gall bladder. Raw pulp and pumpkin juice will be very beneficial for your health.
Types of pumpkin with photos: history and homeland
Large-fruited pumpkin
This type of pumpkin is native to the mountainous regions of Peru, Bolivia, and Ecuador (South America). Description of pumpkin: the stem of a large-fruited pumpkin is cylindrical, the stalk is rounded, with hairy pubescence.
The leaves of the large-fruited pumpkin are kidney-shaped and five-lobed.
The seeds are white or pale cream, large, without the rim characteristic of many pumpkins. Compared to other types, it is less demanding of heat. It is grown both for food purposes and for livestock feed. Large-fruited pumpkin is more common in the south of our country.
A photo of this type of pumpkin can be seen above.
Hard-bark pumpkin (table)
This type of pumpkin originates from the mountainous regions of Central America.
Its fruits have a hard bark. In the middle zone, hard-bark pumpkin is more common than other types. It does not always ripen; it is ripened during storage.
The structure of a pumpkin: its stem is sharply faceted, grooved, with awl-shaped pubescence, like the stalk. The leaves are five-lobed and pointed.
The seeds of the hard-barked pumpkin are yellow-white, medium in size, with a clearly defined rim.
They eat young ovaries, which they begin to harvest in the summer. Hence their name - summer squash. They are also called bush pumpkins because their vines are very short and they grow like a bush. Above you can see a photo of this type of pumpkin.
butternut squash
From the history of pumpkin you can learn that this species comes from Central America, or rather, the homeland of this pumpkin is the coastal areas. It requires more heat, but is sweeter and tasty compared to other types of pumpkins. In our area it is cultivated only by individual amateurs.
Varieties of butternut squash vary in fruit shape: oval, flat, club-shaped and elongated. The varieties also differ in the color of the fruit: pinkish, dark brown, grayish, etc.
The stem of the nutmeg pumpkin is blunt-faced, the pubescence on the stem is finely fibrous. The leaves are kidney-shaped with 5–7 serrated lobes.
White spots and stains are observed on the leaves of butternut squash. The seeds are medium in size, off-white with a rim darker than the seed. Species do not cross with each other, and varieties of the same species and variety can easily cross-pollinate. The resulting hybrids are often infertile.
Characteristics of the pumpkin plant
The structure of a pumpkin: the stem of a pumpkin has the appearance of a creeping vine. Its length reaches an average of 5–10 m. Branching, it produces up to four orders of lateral shoots over the summer. Summer pumpkins have a short stem - no more than 40–50 cm. Additional roots form on the stem when it comes into contact with moist soil.
The main root of the pumpkin plant is a taproot, penetrates deep into the subsoil and is highly branched. The total length of the root along with branching, according to Academician V.I. Edelynteina, more than 170 m.
The leaves are large, long-petiolate. As V.I. pointed out. Edelyptein about the characteristics of pumpkin, a pumpkin plant at the age of 3–4 months has a leaf surface of more than 30 m2.
In the axils of the leaves there are lateral shoots, tendrils, male and female flowers. They are very large - up to 10 cm in diameter. The flowers open at 5–6 o'clock in the morning and close in the evening. Female flowers bloom for 2–3 days, male flowers for 1 day. Flowers are cross-pollinated by insects.
The fruit is a false berry (pumpkin). In a large-fruited pumpkin it reaches a mass of 80 kg or more. There are small-fruited pumpkins - up to 1 kg. For example, a toy pumpkin weighs only 200–300 g. Mature zucchini fruits weigh on average 2–3 kg, but can be larger; squash fruits are smaller.
The edible part of the fruit of a pumpkin is 30% of the fruit’s weight, and in squash, squash, and crookneck at technical ripeness it is 100%.
The shape of pumpkin fruits is round, rounded-flat, oval, y and kruknek are elongated, and y are flattened.
Pumpkin fruits picked from our gardens usually ripen during storage. At the same time, starch turns into sugars, and the fruits become sweeter. In zucchini, 7–10 day old ovaries are used as food, and in squash, 5–7 day old ovaries are used for food.
Characteristics of pumpkin germination: . Its seeds begin to germinate at a temperature of + 11–14 °C, but this process is more intense at + 25–30 °C. For an adult plant, the optimal temperature is + 25–27 °C. Pumpkin can withstand quite high temperatures. In some varieties of pumpkin, proteins coagulate only at 60 °C and above. Like all heat-loving crops, pumpkin does not tolerate frost. It is also not resistant to prolonged exposure to low positive temperatures.
Pumpkin leaves do not have pubescence, so on hot days they evaporate a lot of water, lose turgor and sag. Thanks to its highly developed root system, pumpkin can withstand prolonged drought. Abundant watering leads to an increase in yield, but at the same time the sugar content in the fruits decreases and the shelf life of the fruits decreases. The optimal soil moisture before pumpkin flowering is 65%, before the first harvest - 70%, and during fruiting - 75% HB.
Pumpkin grows better on soils rich in organic matter and light in mechanical composition. It is very responsive to the application of fresh manure together with mineral fertilizers. Phosphorus fertilizers increase the sugar content of fruits, potassium fertilizers increase their keeping quality and plant resistance to disease, and nitrogen fertilizers increase productivity. The application of nitrogen fertilizers should be approached very carefully. Thus, high doses of nitrogen fertilizers at late dates increase the nitrate content and reduce the amount of sugars in fruits. To avoid this, it is better to add urea rather than ammonium nitrate in fertilizing.
1. Fill out the diagram.
Organs of angiosperms:
- Vegetative - root, shoot.
- Generative - flower, fruit.
2. Complete the laboratory work "Structure of seeds of dicotyledonous plants." Label the parts of a bean seed in the picture.
1 - stalk.
2 - kidney.
3 - spine.
4 - cotyledons.
5 - seed coat.
3. Complete the laboratory work “Structure of the wheat grain.” In the picture p Describe the parts of a wheat grain.
1 - pericarp
2 - endosperm
3 - shield
4 - kidney
5 - stalk
6 - spine
7 - embryo.
Conclusion: Beans are a dicotyledonous plant, therefore they have 2 cotyledons. Wheat is a monocot and has one cotyledon and endosperm.
4. Fill out the table "Comparison of seeds of dicotyledonous and monocotyledonous plants."
5. Compare the parts of the seed and sprout. Show with arrows on the diagram from which parts the corresponding parts of the seedling developed.
Answer: From the bud - the leaves, from the stem - the stem, from the root - the root, from the cotyledons - the first 2 leaves. Conclusion: from each part of the embryo and seed a certain part of the plant develops.
6. Study the structure of an apple, pumpkin or sunflower seed. Sketch the structure of one of the seeds. Analyze the structure of the seed you studied and draw a conclusion.
Answer: A pumpkin seed consists of an embryo, 2 cotyledons, and a seed coat. There is no endosperm. The function of storing substances is performed by the cotyledons. The type of pumpkin seeds is dicotyledonous seeds without endosperm.
In our article we will look at the structure of the seed. Apple trees, wheat, beans, cabbage, sunflowers... It is simply impossible to list all the plants that reproduce using seeds! After all, their total number is more than 300 thousand species. Thanks to what structural features did they occupy a dominant position in the plant world?
Spores and seeds: find the differences
Fungi, bacteria, aquatic plants, and the first land-dwellers reproduce with the help of other specialized structures. They are called spores. These are oval or elliptical shaped cells. They consist of a double shell, cytoplasm, chromosomes and an apparatus for protein synthesis.
What is the advantage of seeds compared to spores? First of all, the latter are multicellular structures. Each of us is familiar with the structure of an apple tree seed. On the outside, it is covered not with a shell, but with a peel. This increases the level of protection for internal contents.
The seed contains a supply of nutrients necessary for the development of the future plant organism. The cytoplasm of the spores is devoid of them. Such structural features provide seed plants with greater viability.
Overall plan
Study the structure of the seed of an apple tree, pumpkin or bean - and you will see that they all have a common plan. The required parts are the peel, germ and endosperm.
The seed is formed as a result of the fertilization process. In gymnosperms, this process occurs in shoot modifications - cones. Their seeds develop on bare or open scales. This is where the name of this group of plants comes from.
A characteristic feature of flowering, or angiosperm, plants is double fertilization. This process was first described by the Russian embryologist and cytologist Sergei Navashin.
Male gametes, or pollen, are found in the stamens of a flower. But in the ovary of the pistil, which is its most expanded part, two specialized cells are formed at once. This is the female gamete and the central germinal one. Two sperm take part in the fertilization process. The first one fertilizes the egg. As a result, an embryo is formed. The second sperm fuses with the central germ cell. This is how the endosperm is formed - a supply of substances necessary for development.
Testa
If you visually examine the structure of an apple tree seed, you can see with the naked eye how dense its cover is. Its origin is possible in two ways. In the first case, this is the result of the development of the integument of the ovule, in the second - the growth of its basal part, the chalaza.
On almost every seed you can see a small scar. Where might it come from? It remains at the site of attachment to the achene, which is also called the funiculus.
Endosperm
The structure of an apple seed demonstrates that the embryo is immersed in a special nutrient tissue. This is the endosperm. Its large cells are rich in organic substances: proteins, lipids, polysaccharides. In the seeds of different plants, the amount of these substances may vary. For example, cereals are rich in starch, but have virtually no lipids. But the seeds of sesame, sunflower, flax, peanuts are a real storehouse of oils - vegetable fats. Man has been using them in his economic activities for a long time.
Germ
This part of the seed develops directly from the fusion of germ cells. The embryo, or embryo, consists mainly of cells of educational tissue. They are young, constantly dividing, and capable of differentiation. This means that cells of any tissue are formed from them.
Cereals, Alliums, Liliaceae are the names of the families of Monocots. They have one cotyledon in the seed embryo, a fibrous root system in the form of a bunch, simple leaves with parallel or arched veins. Since Monocots lack a cambium in their stems, only grasses are found among them.
The embryo contains all the parts of the future plant, only in miniature. These are the root, bud, stem and leaves. During germination, you can study the structure of the seed in development. An apple tree, pumpkin or sunflower will have two embryonic leaves on the surface. They are also characterized by the presence of simple or complex leaves with reticulate venation and lateral educational tissue - cambium. The root system of such plants is taproot. The presence of two cotyledons is a structural feature of apple and pumpkin seeds.
Figure: biology and physiology of plants
Certain factors are necessary for seed germination and embryo development. After all, some plants’ seeds can be stored and not spoil for a long time. What's the secret? Naturally, there are conditions. First of all, water is needed. The fact is that endosperm nutrients can only dissolve in liquid. Under its influence, the seeds begin to swell and their skins begin to tear. The embryonic root begins to develop first, followed by the stem.
Air access is also necessary for a developing plant, since tissues need oxygen for respiration. It is also important to take into account the temperature regime. But this factor is quite individual. For plants in temperate latitudes, the temperature comfortable for seed germination is + 10, 12 degrees. But winter wheat under such conditions will not produce a harvest. Its seeds will begin to germinate at +1.2 degrees Celsius.
We hope that now everyone will be able to draw the structure of an apple tree seed and draw a conclusion about the general features of the structure of this generative organ of plants. Its components are the germ, endosperm and peel. Each of them performs certain functions, which together ensure the development of a plant from a seed.