Male sex cells - sperm - are formed in the dust particles of pollen that develop in the anthers of the stamens of the flower. Usually, pollen consists of many dust particles (pollen grains) connected in groups. In dust particles, sperm are formed - male germ cells.
Female reproductive cells - eggs - are formed in the ovules located in the ovary of the pistil of the flower (flowering plants have ovaries with one or more ovules). In order for seeds to develop from all the ovules, it is necessary to deliver sperm to each ovule to the eggs, since each egg is fertilized by a separate sperm.
The process of fertilization in plants is preceded by pollination. As soon as a speck of dust hits the stigma of the pistil (with the help of wind or insects), it begins to germinate. One of its walls stretches and forms a pollen tube. At the same time, two spermatozoa are formed in the dust grain. They move to the tip of the pollen tube. Moving through the tissues of the stigma and style, the pollen tube reaches the ovary and penetrates into the ovule.
By this time, in the ovule, in its middle part, one cell divides and greatly elongates, forming the so-called embryo sac. In it, at one end is an egg, and in the center is a cell with two nuclei, which soon merge, forming one - the central nucleus. Having penetrated the ovule, the pollen tube germinates into the embryo sac, and there one sperm merges (combines) with the egg, forming a zygote, from which the embryo of a new plant develops.
Another sperm that has entered the embryo sac fuses with the central nucleus. The resulting cell divides very quickly, and soon a nutrient tissue, the endosperm, is formed from it.
The fusion in the embryo sac of sperm - one with the egg and the other with the central nucleus is called double fertilization.
The process of double fertilization is a phenomenon peculiar only to flowering plants. Thanks to double fertilization, the embryo of a new plant receives a very valuable endosperm with nutrients.
There is another classification:
13. Structure and functions of a flower.
Flower - reproductive organ of angiosperms. The flower consists of a pedicel, receptacle, perianth, androecium and gynoecium.
Fertile parts of a flower (stamen, pistil).
Sterile parts of the flower (calyx, corolla, perianth).
flower functions.
A flower is a modified shortened shoot adapted for the reproduction of angiosperms (flowering) plants.
The exclusive role of the flower is due to the fact that it combines all the processes of asexual and sexual reproduction, while in lower and many higher plants they are separated. In a bisexual flower, micro- and megasporogenesis, micro- and megagametogenesis, pollination, fertilization, and the formation of seeds and fruits are carried out. The peculiarities of the structure of the flower make it possible to carry out the listed functions with minimal expenditure of plastic substances and energy.
The central (main) parts of the flower. Most plants have one or more pistils in the center of the flower. Each pistil consists of three parts: ovary - expanded base; column - more or less elongated middle part; stigma - the top of the pistil. Inside the ovary are one or more ovules. Outside, the ovule is surrounded by integuments through which a narrow channel passes - the pollen entrance.
Around the pistil (or pistils) are stamens. Their number in a flower is different in flowering plants: in wild radish - 6, in clover - 10, in cherry - a lot (about 30). The stamen consists of two anthers and a filament. Pollen develops inside the anther. Individual dust grains are usually very small grains. They are called pollen grains. The largest pollen grains reach 0.5 mm in diameter.
Perianth. In most flowers, the pistils and stamens are surrounded by a perianth. In cherries, peas, buttercups, the perianth consists of a corolla (a set of petals) and a calyx (a set of sepals). Such a perianth is called double. In a tulip, lily, lily of the valley, all the leaves are the same. Such a perianth is called simple.
Flowers with double perianth
Flowers with simple perianth
The tepals may grow together or remain free. In the tulip and lily, the perianth is simple, separate-leaved, and in the lily of the valley, it is joint-leaved. Flowers with a double perianth may also have fused sepals and petals. Primrose flowers, for example, have a calyx and a corolla. Cherry ranunculus flowers have a single-leaved calyx and a single-petaled corolla. The bell has a separate-leaved calyx, and the corolla has a joint-petal.
The flowers of some plants do not have a developed perianth. For example, in willow flowers, it resembles scales.
Inflorescences and flowers of willow
flower formula. The structural features of the flower can be noted in abbreviated form in the form of a formula. The following abbreviations are used in its compilation:
Ok - leaves of a simple perianth,
H - sepals, L - petals, T - stamens, P - pistils.
The number of flower parts is indicated by numbers in the form of an index (Ch5 is 5 sepals), with a large number of flower parts, the sign ∞ is used. In the case of fusion of parts with each other, the number indicating their number is enclosed in brackets (L (5) - the corolla consists of 5 fused petals). If the parts of the flower with the same name are located in several circles, then a + sign is placed between the numbers indicating their number in each circle (T5 + 5 - 10 stamens in the flower are located 5 in two circles). For example, the lily flower formula- Ok3+3T3+3P1, bell- CH5L(5)T5P1.
Receptacle. All parts of the flower (near the flower garden, stamens, pistils) are located on the receptacle - the overgrown axial part of the flower. Most flowers have a pedicel. She moves away from the stem and connects it to the flower. In some plants (wheat, clover, plantain), pedicels are not expressed. Such flowers are called sessile.
Flowers bisexual and unisexual. Usually in one flower there are both pistil (pistils) and stamens. Such flowers are called bisexual. Some plants (willow, poplar, corn) have only pistil or stamens in the flower. Such flowers are called same-sex - staminate or pistillate (Fig. 71).
Monoecious and dioecious plants. In birch, corn, cucumber, same-sex flowers (staminate and pistillate) are located on one plant. Such plants are called monoecious. In poplar, willow, sea buckthorn, stinging nettle, some plants have only staminate flowers, while others have pistillate ones. These are dioecious plants.
The ovary is the empty lower thickened part of the pistil, the female reproductive organ of plants.
It provides protection and fertilization of ovules (ovules), from which seeds are formed.
The pistil is located in the flower and consists of the stigma, which traps the pollen, the style, along which the pollen enters, and the ovary, where the seeds develop. After fertilization, a fetus is formed from it.
In the central part of the ovule (nucellus) are eggs, in the case of pollination, they are fertilized, and seeds develop from them. In the same place, an embryo sac is formed, due to which they will feed.
Ovary functions
- Inside the ovary, the process of fertilization and seed maturation takes place;
- Protects ovules from external harmful environmental factors (temperature changes, drought, eating by insects, rain, etc.);
- Maintains the right level of moisture;
- Provides seed nutrition;
- It is the basis of the future fetus.
Ovary types
According to the number of nests, that is, the existing cavities separated by partitions in which the seeds are located, the ovary is single or multi-celled.
I - one-celled ovary, II - two-celled ovary, III - five-celled ovary. In all figures: 1 - ovary wall; 2 - nest; a - ovules, 4 - placenta.
Another classification of ovaries is based on their location in relation to the receptacle.
The receptacle is the lower part of the flower, that is, its base, on which the petals, sepals, stamens and pistils are located.
According to the type of location, the ovary can be:
- Upper or free - located above the receptacle. It does not grow together with other parts of the flower, while the flower is called pistillate (cereal, ranunculus, legume, etc.);
- The lower one is under the receptacle, the flower is attached to the top of the ovary, therefore it is called suprapestival (composite, cactus, orchid, etc.);
- Semi-lower - grows together with the flower, but not at the very top, the flower is called semi-pistillate (saxifrageous).
The formation of fruits from the ovary
Fruits, depending on the type of formation from the ovary, are divided into several types: 1. Real - are formed only by the ovary. Are divided into:
- Simple, formed by one pestle (cherry, plum, bird cherry, acacia bean);
- Complex, formed by several fused pistils (raspberries, blackberries)
- Fractional fruits are formed by a multi-celled ovary with partitions (forget-me-not, basil, lavender, thyme, etc.);
2. False - are formed with the participation of other parts of the flower, such as the receptacle and perianth, including petals and sepals.
note
It is easy to distinguish false ones from real ones by the remains of flower parts (apples, pears).
Causes of damage to the ovary
Damage to the ovary can lead to the absence of seeds and even fruits in the future. Damage can be caused by:
- Late spring frosts during flowering, in which the flowers and fruit set are showered. If the ovaries were partially damaged, then deformed, small, or unusable fruits develop from them;
- The absence or a small number of pollinators, while some of the flowers remain unfertilized, therefore they are discarded;
- Poor soil and lack of watering, when the plant does not have enough substances to grow all the ovaries that have appeared. In this case, it is necessary to apply complex mineral and organic fertilizers and provide watering during a drought;
- Pests (codling moth, apple sawfly, flower beetle, etc.). To get rid of them, you do not need to resort to artificial insect repellents, as they will also have a detrimental effect on pollinating insects. It is better to spray the plants with decoctions of herbs that repel pests (nettle, dandelion, garlic, wormwood, etc.)
- Leaf diseases. Healthy leaves are necessary to provide the plant with the necessary substances; without them, the ripening of fruits and seeds is impossible;
- Overloading with the number of fruits: with a large number of ovaries formed, the plant cannot feed them all, therefore it discards a part. Timely thinning of flowers will help to avoid this process.
All-Russian Olympiad for schoolchildren
2015-2016 academic year
school stage
Biology, grade 11
Tasks
Maximum score - 90.5
Part I You are offered test tasks that require you to select only one answer
out of four possible. The maximum number of points that can be scored is 30
(1 point for each test task). The answer index you think is the most
complete and correct, indicate in the answer matrix.
1. In flowering plants, the following develops from the wall of the ovary:
a) an embryo;
b) seed coat;
c) endosperm;
d) pericarp.
2. Algae, which, thanks to their pigments, are most adapted to photosynthesis at great depths:
a) green
b) red;
c) brown;
d) golden.
3. Functions of the root cap in plants:
a) ensuring the growth of the root in length;
b) holding water and solutions of mineral substances;
c) protection of the root tip from damage;
d) absorption of water and solutions of mineral substances.
4. Name the type of fruit in potatoes:
a) tuber;
b) berry;
c) a box
d) a seed.
5. Which plant has a fibrous root system:
a) beets;
b) sunflower;
c) tulip;
d) peas.
6. Same-sex flowers are typical for:
a) pumpkins
b) wheat;
c) peas;
d) rye.
7. What set of chromosomes is found in the endosperm cells in the wheat seed?
a) haploid; b) diploid; c) triploid; d) polyploid.
8. Spike inflorescence is typical for:
a) dill; b) plantain; c) lily of the valley; d) gladiolus.
9 Bacteria are the causative agents of:
a) scabies; b) hepatitis; c) cholera; d) malaria.
10. Which of the formations by origin is not a derivative of the skin epidermis:
a) whalebone b) rhinoceros horn; c) pangolin scales; d) cat vibrissae
a) bull tapeworm; b) roundworm; c) pork tapeworm; d) echinococcus.
12. Which of the following organisms exhibits positive phototaxis:
a) chlorella; b) malarial plasmodium; c) euglena d) amoeba-proteus.
13. Insects with complete metamorphosis include:
a) orthoptera, diptera; b) hemiptera, homoptera; c) Coleoptera, Lepidoptera; d) Hymenoptera, dragonflies.
14. Roundworms differ from flatworms by the presence of:
a) the nervous system; b) anus; c) cuticles; d) excretory system.
15. The figure shows the skeleton of a vertebrate.
In its structure it is impossible to find:
a) the cranium;
b) chest;
c) cervical vertebrae;
d) ribs.
16. Malaria is caused by:
a) amoeba; b) trypanosomes; c) plasmodia; d) ciliates.
17. The intestine is absent in:
a) liver fluke; b) a wide ribbon; c) pinworms; d) roundworm.
18. Human erythrocytes are destroyed in:
a) thymus b) yellow bone marrow c) liver d) pancreas.
19. Of the listed enzymes in the small intestine does not function:
a) chymotrypsin; b) lipase; c) pepsin; d) pancreatic amylase
20. Therapeutic serum is:
a) an antibody preparation b) weakened bacteria c) a suspension of leukocytes d) an antibiotic solution.
21. Cartilaginous semirings form the basis of the skeleton:
a) trachea b) esophagus c) larynx d) bronchioles.
22. The composition of the anterior roots of the spinal cord includes axons:
a) conducting impulses from the brain b) motor neurons c) sensory neurons d) intercalary neurons.
23. The unpaired bone of the skull is:
a) maxillary b) occipital c) parietal d) temporal.
24. The human respiratory center is located in:
a) cerebral cortex b) diencephalon c) medulla oblongata d) cervical segments of the spinal cord.
25. Mucus covering the walls of the stomach:
a) inactivates saliva enzymes b) softens food c) promotes the conversion of pepsinogen into pepsin d) prevents self-digestion of the stomach walls.
26. The first stage of embryonic development is called:
a) neurula; b) blastula; c) crushing; d) gastrula.
27. Examples of homologous organs are:
a) the dorsal fin of a shark and a dolphin;
b) digging limb of a mole and a bear;
c) the pectoral fin of a perch and a human hand;
d) tortoise shell and snail shell.
28. According to the results of genetic analysis by the wild ancestor of the domestic cat
are at least five representatives of one of the subspecies:
a) European cat;
b) forest cat;
c) reed cat;
d) a Chinese cat.
29. In ecosystems of great depths of the ocean, there are necessarily:
a) animals, microorganisms; b) plants, microorganisms; c) plants, animals, microorganisms; d) plants and animals.
30. Interactions of individuals in a population, between populations are called:
a) abiotic factors; b) biotic factors; c) anthropogenic factors;
d) evolutionary factors.
31. The divergence of daughter chromatids to the poles occurs in meiosis in:
a) prophase I;
b) metaphase II;
c) anaphase I;
d) anaphase II.
32. What happens in an ecosystem if there are no decomposers in it or their activity is poorly expressed:
a) nothing happens
b) there is an accumulation of organic matter;
c) the number of producers decreases,
d) the number of consumers increases.
33. When crossing a red cat with a tortoiseshell cat in offspring:
a) all kittens will be black;
b) half of the kittens will be red;
c) all cats will be red;
d) all cats will be black.
34. In the body of animals, an oxygen molecule does not bind to:
a) myoglobin;
b) hemoglobin;
c) cytochrome c;
d) cytochrome a3.
35. Of the listed ecosystems, the lowest production per square meter are:
a) meadow;
b) taiga;
c) tropical forest;
d) open ocean.
Part II. You are offered test tasks with one answer option out of four possible, but requiring a preliminary multiple choice. The maximum number of points that can be scored is 20 (2 points for each test task). The index of the answer that you consider the most complete and correct, indicate in the answer matrix.
1. Mushrooms with animals bring together signs:
1) the only posterior flagellum in motile cells;
2) autotrophic type of nutrition;
3) store glycogen;
4) the ability to unlimited growth;
5) the presence of chitin.
a) 1, 2, 3;
b) 1, 2, 4;
c) 1, 3, 5;
d) 2, 3, 4;
e) 2, 3, 5.
2. The following compounds are involved in the regulation of blood sugar levels:
1) glucagon;
2) insulin;
3) prolactin;
4) testosterone;
5) estradiol.
a) only 1, 2;
b) only 1, 5;
c) only 2, 3;
d) only 2, 4;
e) 1, 2, 3.
3. The processes of plastic exchange include:
1) ATP synthesis;
2) photosynthesis;
3) protein synthesis;
4) glycolysis;
5) synthesis of nucleotides.
a) 1, 2, 3;
b) 2, 3, 4;
c) 2, 3, 5;
d) 2, 4, 5;
e) 3, 4, 5.
4. Indicators of biological regression are:
1) reduced life expectancy;
2) increase in embryonic mortality;
3) decrease in species diversity;
4) reduced fertility;
5) size reduction.
a) only 3;
b) only 1, 3;
c) only 1, 2, 3;
d) only 2, 3, 5;
e) 1, 2, 3, 4.
5. From the Central American Center of Origin (according to N.I. Vavilov)
cultivated plants occur:
1) wheat;
2) corn;
3) rice;
4) soy;
5) sunflower.
a) only 1, 3;
b) only 1, 5;
c) only 2, 5;
d) only 1, 2, 5;
e) 2, 3, 5.
6. Remote hybridization in animals is difficult due to:
1) a different set of genes in different species;
2) a different set of chromosomes in different species;
3) tissue incompatibility of different types;
4) different habitat conditions of species;
5) different mating behavior of species.
a) only 1, 3;
b) only 1, 5;
c) only 2, 5;
d) only 1, 3, 4;
e) 2, 4, 5.
7. In eukaryotes, transcription occurs in:
1) core;
2) the Golgi apparatus;
3) mitochondria;
4) plastids;
5) lysosomes.
a) 1, 2, 3;
b) 1, 2, 4;
c) 1, 2, 5;
d) 1, 3, 4;
e) 1, 3, 5.
8. One codon of messenger RNA can encode:
1) one amino acid;
2) two amino acids;
3) three amino acids
4) four amino acids;
5) not a single amino acid.
a) only 1, 2;
b) only 1, 3;
c) only 1, 4;
d) only 1, 5;
e) 1, 2, 5.
9. Of the listed processes in mitochondria, the following occurs:
1) protein synthesis;
2) DNA synthesis;
3) synthesis of fatty acids;
4) ATP synthesis;
5) oxidation of fatty acids.
a) only 3;
b) only 2, 4;
c) only 1, 3, 4;
d) only 1, 4, 5;
e) 1, 2, 4, 5.
10. Lipids are part of :
1) ribosome;
2) mitochondria;
3) chromatin;
4) nucleolus;
5) Golgi apparatus.
a) 1, 2;
b) 1.5;
c) 2, 3;
d) 2, 4;
e) 2, 5.
Part 3 You are offered test tasks in the form of judgments, with each of which you must either agree or reject. In the response matrix, indicate the answer option "yes" or "no". The maximum number of points that can be scored is 20 (1 point for each test item).
1. The bulk of pine wood is made up of vessels and mechanical fibers.
2. The products of photosynthesis move down the sieve tubes.
3. In the vein of the leaf, the phloem is located below, and the xylem is above.
4. Oxygen is released by all green plants.
5. Plant roots can carry out photosynthesis.
6. Cockroach blood is colorless because it does not contain hemoglobin.
7. All ciliates have contractile vacuoles.
8. Kamchatka crab is a hermit crab, which is characterized by a weak development of the abdominal region.
9. Lungfish - an extinct group of fish from which terrestrial vertebrates originated.
10. A characteristic feature of mammals is live birth.
11. The main organ that, under the influence of the hormone insulin, provides a decrease in the level of glucose in human blood is the liver.
12. Oxygen and carbon dioxide are transported by blood only due to binding to hemoglobin and transfer as part of the hemoglobin-gas molecule complex.
13. The liver is able to quickly and without serious consequences regenerate up to 70% of its volume removed during surgery.
14. The basis of biological membranes is a double layer of phospholipids.
15. The largest molecules in living organisms are muscle proteins.
16. The products of the dark stage of photosynthesis are glucose and oxygen.
17. Compounds indispensable for the human body include amino acids and nitrogenous bases.
18. In terrestrial ecosystems, the highest density of plant biomass is found in tropical forests.
19. The absence of intestines in tapeworms indicates a biological regression of this group of animals.
20. Mitochondria and lysosomes appeared in eukaryotic cells as a result of symbiosis.
Part 4 You are offered test tasks that require compliance. The maximum number of points that can be scored is 15.5. Complete the answer matrices as required by the assignments.
( max . 3.5 points)
Before you is a section of the stem of a plant. Correlate the main structures of the conducting beam (A-Zh) with their designations in the figure (1-7).
A - the main parenchyma; B - sieve tubes; B, companion cells;
G - spiral vessel; D - sclerenchyma; E - porous vessel;
G - ringed vessel.
Notation
1
2
3
4
5
6
7
structures
2. ( max . 4 points)
The figure shows representatives of the fauna of the forest floor and upper soil horizons.
Establish a correspondence between organisms (1-8) and taxa to which they belong (A–E): A) Centipedes; B) arachnids; B) the simplest; D) crustaceans; D) insects.
organisms
1
2
3
4
5
6
7
8
taxa
3. ( max . 3 points)
Which of the following structures are indicated in the figure by numbers 1 - 5?
A - bladder, B - kidney; B - kidney cortex; D - medulla of the kidney; D - renal pelvis; E - ureter.
room
1
2
3
4
5
6
organ
4. ( max . 2.5 points)
For each product in the right column, find the corresponding substance in the left column.
A. Sucrose
1. Beef liver
B. Lipids
2. Beetroot
B. lactose
3. Fish oil
G. Glycogen
4. Pea grains
D. Protein
5. Milk
1
2
3
4
5
5. ( max . 2.5 points)
Many species of arthropods are closely related to man and his dwelling (1-5). Select from the list (A-E) the type of relationship that arises with the person.
1 - Housefly (Musca domestica)
2 - Bed bug (Cimex lectularius)
3 – Black(Blatta orientalis)and ginger(Blatella germanica)cockroaches
4 – Home spider(Tegenaria domestica)
5 – mosquitoes kindCulex (urban the form– C. pipiens f. molestus)
A) proto-operation
B) commensalism
B) neutralism
D) symbiosis
1
2
3
4
5
Member of the subject-methodical commission: /Skorykh S.A./
Flowering plants are a large and diverse group that dominates most terrestrial ecosystems. From the main flowering plants cultivated by man, his existence depends. But in order for flowering plants to appear, they must go through the stage of pollination and fertilization. How this happens, read this article.
Pollination
This process is carried out by the transfer of pollen from the stamens to the pistil. How do pollination and fertilization occur in flowering plants? This is done in two ways: self-pollination and cross-pollination. In the first case, the transfer of pollen grains to the pistil occurs in the same flower. This is how peas or tulips are pollinated. In cross-pollination, pollen from a flower of one plant is transferred to the pistil of another. most often by insects, in rare cases - by wind (sedge and birch), birds and water.
As a result of pollination by insects, bright, highly visible flowers with a pleasant smell and nectaries that produce a sweet liquid are formed. These plants also produce a lot of pollen. It is food for insects. They are attracted by the bright color or smell of the flowers. When insects extract nectar, they touch the surface of pollen grains that stick to their body, and when they fly to the flower of another plant, they remain on the pistil. This is how insect pollination works. Many are pollinated only by a certain insect: fragrant tobacco - by a night butterfly, creeping clover - by a bee, and meadow clover - by a bumblebee.
Cross-pollinated plants are better adapted to changing environmental conditions. But the process of pollination in this case depends on a number of factors. And self-pollination does not depend on anything. He is not afraid of weather conditions and the absence of intermediaries.
Fertilization
A grain of pollen, falling on the stigma of the pistil, begins to germinate gradually. A long pollen tube develops from the vegetative cell. Growing up, it reaches the level of the ovary, and then the ovule. At the same time, a pair of sperm is formed, which penetrates the pollen tube. She, in turn, enters the ovule through the pollen passage. Then the tube at the very tip breaks and releases the male sperm, which are immediately sent to the embryonic membrane, which is called the sac. This is where the eggs develop.
Next, the egg is fertilized with one sperm, and the formation of a zygote, from which a small embryo of a completely new organism of plant origin begins to form. At the same time, the second sperm fuses with the nucleus of the zygote or with the polar nuclei. As a result, a triploid cell is formed, from which the endosperm arises. It is called a nutrient tissue, which contains reserves of the necessary substances for the normal development of the embryo of a future plant. This is how the organs of sexual reproduction of flowering plants are represented.
When one sperm cell with an ovum, and the other with polar nuclei, merge together, this process is called It is peculiar only to flowering plants and is a unique feature of angiosperms. The fertilized ovule grows into a seed. As a result, the ovary of the pistil grows. In flowering plants, a fruit develops from the wall of the ovary.
reproduction
Any plant, reaching a certain size and having passed the appropriate stages of development, begins to reproduce organisms of a similar species. This is reproduction, which is a necessary property of life. All organisms thus prolong the existence of the species itself. Distinguish sexual and which occurs with the participation of one individual. When plants develop specialized cells - spores, organisms begin to multiply.
Mosses, algae, ferns, club mosses and horsetails. Spores are special small cells with a nucleus and cytoplasm, which are covered with a membrane. They are able to endure bad conditions for a long time. But, getting into a favorable environment, they quickly germinate and begin to form daughter plants, the properties of which do not differ from the mother ones.
During sexual reproduction, female and male germ cells merge, resulting in the formation of daughter organisms that are qualitatively different from the parent. Here the parental organisms of the feminine and masculine are already taking part.
The macrosporangium plays a dominant role in the composition of the ovule. It is in it that the laying of one mother cell occurs, from which macrospores are formed. Three things begin to die off, and eventually collapse. The fourth macrospore is feminine, elongates and its nucleus divides. Then the daughter nuclei move to different poles of the elongated cell. Each nucleus formed is further divided twice.
In cells located near different poles, four nuclei are formed. This is called the embryo sac, in which there are eight haploid nuclei. Further, from each four nuclei, one of them follows to the center of the embryonic sac. There they merge, as a result of which they form a secondary nucleus - diploid.
Then, in the embryo sac, in the cytoplasm, partitions are formed between the nuclei at the cellular level. There are seven cells in the bag. Near one of its poles is the egg apparatus, which includes a large egg and two auxiliary cells. At the other pole, antipodal cells are located, there are three in total. So, there are now six in the bag and one diploid, with a secondary nucleus. It is located in the center of the embryonic sac.
What is an ovary?
It is called the lower thickened part of the pistil with a cavity closed inside, in which the ovules are located. Pollen enters from the stigma of the pistil into the ovule, which is protected from adverse conditions by an internal moist cavity. In the ovule, the development of female germ cells - eggs.
What are the ties?
Types of ovaries of flowering plants are:
- Upper. It is attached freely to the receptacle, without growing together with other sections in the flower. The walls of the ovary are formed from the carpels. In flowering plants, a fruit develops from the wall of the ovary. An example is ranunculus and cereal plants. These flowers are called sub-pistillate or near-pistillate.
- The lower ovary is always under the receptacle. It is formed with the participation of other departments of the flower: the base of the sepals and stamens with petals, which in many flowers are attached to the top of the ovary. In flowering plants, a fruit develops from the wall of the ovary. Examples are Compositae, cactus and orchid plants. The flower is called an overspray.
- Semi-inferior ovary. Its top does not grow together with other parts, so it is free. Flowers of this type are called semi-pistillate. These types of ovaries of flowering plants are.
flowering plants
They are the most progressive group of plants, numbering two hundred and fifty thousand species distributed throughout the planet Earth. The smallest plant is duckweed, the diameter of which is one millimeter. She lives in the water. The largest flowering plants are trees reaching a height of one hundred meters or more.
The appearance of flowering plants occurs due to the development of a special reproductive organ - a flower. In some plants, it is painted in bright colors, in others it smells wonderful. The flowers are small and inconspicuous in grass-like plants. Despite the huge variety of flowering plants, they all harmoniously fit into our lives: they decorate gardens and parks, give the joy of communicating with them.
flower structure
A flower is a complex organ system that provides reproduction of plants by seeds. Its appearance led to the wide distribution of angiosperms (flowering) plants on Earth. The flower has many functions. With its participation, stamens with pollen grains, pistils with ovules are formed. It plays a major role in pollination, fertilization, seed and fruit formation.
The flower is a shortened, modified, growth-limited shoot bearing a perianth, pistils, and stamens. All have flowers similar in structure and different in shape. So there is an adaptation to pollination in various ways.
The flower may end in the main or lateral stems, the bare part of which, under the very flower, is called the pedicel. It is greatly shortened or completely absent in sessile flowers. The pedicel passes into the receptacle, which is elongated, convex, concave or flat. It contains all parts of the flower. These are sepals with petals, stamens with a pistil, in the lower part of which an ovary is formed, in which ovules or ovules are located. A flower with such an ovary has a concave receptacle. If the ovary forms at the top of the pistil, the receptacle will be convex or flat.
