Biology lesson “Ontogeny is the individual development of an organism. Abstract of the lesson "individual development of the organism" - abstracts of biology lessons - file directory - biology is not for nerds
Summary of a lesson in biology in grade 10
Topic: Individual development of organisms
Purpose: To create conditions for studying the individual development of organisms.
Tasks: Educational - Update knowledge about the patterns of individual development of organisms on the example of vertebrates, about the stages of embryonic development, about the periods of postembryonic development.
Developing - Develop concepts: ontogenesis, its types, metamorphosis, placenta, morula, blastula, blastocoel, gastrula, neurula, ectoderm, endoderm, mesoderm, embryonic induction, periods of postembryonic development: juvenile, puberty, aging, direct and indirect development.
Educational - To arouse interest in the topic being studied. Cultivate the accuracy of keeping a notebook.
Equipment: CD disk “Virtual School of Cyril and Methodius. Biology. Grade 10", tables: "Individual development using the example of a lancelet."
During the classes
Organization of the lesson
I assess the sanitary and hygienic condition of the class, check the availability of equipment necessary for the lesson. Greetings students:
Hello! Sit down. To begin with, we note who is not in the lesson today.
I note the composition of the class.
We studied the life cycle of a cell, types of cell division, development of germ cells, fertilization. Today in the lesson we will continue to study the section "Reproduction and individual development of organisms."
2 hours
Introduction
Learning new material
What happens after fertilization? We will answer this question in today's lesson. So, write the topic of the lesson in a notebook.
The individual development of organisms is called ontogeny.
Ontogeny is divided into 3 types:
- Larval - In insects, fish, amphibians. The zygote quickly develops into a larva that feeds and grows on its own. Metamorphosis is the transformation of a larva into an adult.
- Oviparous - In reptiles, birds and oviparous mammals. The embryo develops inside the egg, there is no larval stage.
- Intrauterine - In most mammals, including humans. The embryo lingers in the mother's body, a temporary organ is formed - the placenta, through which the mother's body provides all the needs of the growing embryo. Ends with childbearing.
In the 19th century F. Müller and E. Haeckel formulated the biogenetic law: Ontogenesis (individual development) of each individual is a brief and rapid repetition of the phylogeny (historical development) of the species to which this individual belongs.
A.N. Severtsov made a great contribution to the development of this law. He established that in the individual development of animals, signs of embryos are repeated.
- Ontogeny is divided into 2 stages:
embryonic and postembryonic
from the formation of a zygote from birth
From birth to death
Carl Baer formulated the law of germline similarity: "Embryos reveal, already from the earliest stages, a certain general similarity within the limits of the type."
Consider the stages of embryonic development.
In notebook and on the board
In a notebook
CD disc
In notebook and on the board
In notebook and on the board
CD disc
In notebook and on the board
CD disc
In a notebook
Table
Stages of embryonic development
Crushing Blastula Gastrula Neirula
Zygotes
- Cleavage of the zygotebegins immediately in the oviduct. The first division occurs in the vertical plane, 2 identical cells are formed - blastomeres . They divide again, 4 blastomeres are formed. Further, they are all divided in a horizontal plane. Blastomeres divide quickly, do not have time to grow, so a lump of blastomeres - MORULA - no more than a zygote. When there are 32 blastomeres, they form a hollow ball with walls in one row of cells. The cavity inside the blastula is the blastocoel.
After implantation of the embryo (introduction of the blastula into the wall of the uterus), at one of the poles of the blastula, its cells begin to divide faster than at the other, they bulge inside the blastocoel - the process of gastrulation. The second inner layer of embryonic cells is formed from the invagination cells. This double layer ball gastrula.
The next stage is neurula . The formation of important parts of the embryo occurs: the neural tube and the notochord.
Now let's study the germ layers and their derivatives. The text of the textbook on p.133-134.
Formation of germ layers
Ectoderm Endoderm Mesoderm
(outer leaf) (inner) Notochord, muscles
nervous system, future intestines, kidneys,
skin cover, its outgrowths are bone and
organs of vision liver, lungs, cartilage
and hearing. pancreas Skeleton,
Gland. circulatory
System.
All parts of the embryo influence each other, and if this influence is disturbed, then the development of a normal organism does not occur. Such influences are embryonic induction. The role of the inductor is to force the surrounding tissues to develop according to a different “plan”.
In notebook and on the board
CD disc
Conversation
Textbook:
With. 133-134
In notebook and on the board
CD disc
In a notebook
Now consider postembryonic development. Let's start with the periods of this development.
- Periods of postembryonic development:
- Juvenile until the end of puberty. Two ways of development: direct and indirect. body growth.
- Pubertal - a period of maturity. Most of life.
- Aging - general biological regularity inherent in living organisms. At a certain age for each species, changes begin in the body that reduce the ability of this organism to adapt to changing conditions of existence.
Death is the cessation of life of an organism. Without death, there would be no generational change - one of the main driving forces of evolution.
Postembryonic development is divided into direct and indirect. Find definitions for these concepts in the text of the textbook on p.136. Record the answer in the form of a diagram:
Postembryonic development
Direct Indirect
A born organism has Formed at first
all major organs, a larva that differs
peculiar to an adult from an adult organism
animal (fish, (flat and ringed
reptiles, worms, insects,
birds, mammals). amphibians, crustaceans
Nye).
Consolidation of the studied material
Complete the written assignments from textbook No. 5 on p. 135, No. 3 on p. 137.
I check student answers. We discuss the studied topic together with the class, answer the question: What happens after fertilization?
In notebook and on the board
CD disc
Textbook:
p.136
In notebook and on the board
CD disc
In a notebook
Textbook:
No. 5 p. 135,
No. 3 p. 137
Generalization of the lesson
I suggest that students write down their homework in their diaries or notebooks:
Study ξ 35, 36, 37.
Prepare for the control work on the section: "Reproduction and individual development of organisms."
I give grades for the lesson.
D/Z
Biology lesson number 17 in grade 9. "_____" ______________ 20____
Individual development of organisms - ontogeny.
Target. To form knowledge about the essence of ontogeny and its stages.
Tasks.
Educational: consider and study the features of ontogeny, stages of development
germ and change occurring at each stage. Get to know the embryonic
postembryonic developmental processes.
Developing: to develop the intellectual and creative abilities of students;
stimulate the cognitive activity of children, develop interest in the subject, ingenuity,
erudition, the ability to quickly and clearly articulate and express their thoughts
Educational: to educate students in diligence, accuracy and responsibility,
love and interest in the subject
During the classes.
1. Org. moment.
2. Repetition of the studied material.
Oral survey:
1. What is meiosis?
(Meiosis (Greek "meiosis" - reduction) is a cell division in which from
one mother cell with a diploid set (2n) of chromosomes produces 4
cells with a haploid (n) set of chromosomes).
2. What processes are based on meiosis in nature?
(4 heterogeneous haploid cells (nc) are formed;
Maintaining a constant number of chromosomes from generation to generation; One of
mechanisms of variability as a result of:
Recombination of genes in prophase I at the entrance of conjugation and crossing over;
Independent divergence of chromosomes).
3. Specify the characteristic differences between mitosis and meiosis.
4. What is crossing over, its meaning.
(Crossing over, break and exchange of sections between some
homologous chromosomes. Significance of recombination of paternal and
maternal genetic material, the source of combinative variability in
new generation).
3. Learning a new topic.
Each organism undergoes significant transformations over the entire period of life:
grows, develops. It can be said that it develops individually. So here's the development
organism from zygote to natural death is called individual development
or ontogeny. Write down the topic of today's lesson "Individual Development
ontogenesis"
Ontogeny - the individual development of organisms - a set of transformations,
occurring in the body from birth to natural death.
Ontogeny in unicellular organisms consists in the fact that the daughter cells that have arisen after division
individuals grow, and the organelles of the maternal organism are replaced in them. During
ontogenesis in unicellular (as well as in multicellular) in response to changing conditions
environment, proteins are synthesized, sensitivity to various
environmental factors.
In the individual development of multicellular organisms, several stages are distinguished,
which are often referred to as age periods. What are these periods?
Ontogenesis
Unicellular Multicellular
cell life cycle from zygote formation to death:
a) embryonic
b) postembryonic
1) The embryonic period is the development of the embryo from the moment of its formation
before birth.
the following tasks:
Milestones of development
germ
Their characteristic
"Organogenesis"
germ layers
Organs, organ system
ectoderm
mesoderm
Endoderm
Skin, skin glands, neural tube - dorsal and
brain, sense organs.
Skeleton, muscles, circulatory and excretory
systems.
Alimentary canal, liver, lungs.
2) The impact of environmental factors on the development of the embryo.
Various mutagens can affect the development of the embryo: alcohol,
nicotine, drugs, drugs. For example, the use of the hypnotic thalidomide in
Western Europe in the 50s led to the birth of several thousand freaks from mothers,
who were taking sleeping pills.
A lack of vitamin B can cause a number of morphological deformities and
internal organs (heart, liver). An excess of certain hormones can become
cause of the developmental anomaly.
Student messages.
3) The postembryonic period is the period of development from the moment of birth to its
of death.
There are two main types of postembryonic development.
Direct, in which the born individual has the same structure as the adult organism
and differs only in smaller sizes. (cockroaches, humans, mammals, birds,
bedbugs).
There are a) non-larval (ovipositor) type, in which the embryo develops
inside the egg (fish, birds) and b) intrauterine type, in which the embryo develops
inside the mother's body.
Indirect, in which the larva is very different from the adult in structure, image
life, nutrition, movement, are not capable of reproduction. (amphibians, beetles,
lepidoptera, flies, bees)
Exercise. Fill in the table, marking the presence of certain stages of development with a “+” sign.
Orthopteran Lepidoptera Fish
Amphibious Birds
Human
Zygote
Larva
chrysalis
adult
individual
4. Fixing.
1. What is ontogeny?
2. What stages can be distinguished in the ontogeny of animals and plants?
3.Give an answer:
Individual development of the organism (ontogenesis)
Fertilized egg (zygote)
A series of mitotic divisions following each other (crushing)
Spherical single-layer embryo with a cavity inside (blastula)
Two-layer embryo with a cavity inside (gastrula)
The outer layer of cells of a two-layer embryo (ectoderm)
The inner layer of cells of a two-layer embryo (endoderm)
Third germ layer (mesoderm)
5. Homework.
§ 16, prepare for the test
Exercise. Read the text "Embryonic development of the organism" and complete
the following tasks:
1. Fill in the table "Stages of embryonic development".
Milestones of development
germ
Their characteristic
2. Characteristics of germ layers.
"Organogenesis"
germ layers
Organs, organ system
ectoderm
mesoderm
Endoderm
3. Fill in the table, marking the presence of certain stages of development with a “+” sign.
Orthopteran Lepidoptera Fish
Amphibious Birds
Human
Zygote
Larva
chrysalis
adult
individual
Embryonic development of organisms.
The study of the embryonic development of organisms is the science of embryology (from the Greek.
embryon - embryo).
During embryonic development, differentiation occurs in structure and function.
cells and organs: histogenesis and organogenesis.
The embryonic period in its development goes through three successive stages:
cleavage, gastrulation, histogenesis and organogenesis.
Features of embryonic development can be more conveniently and more clearly seen on the example
lancelet, since it has small eggs and relatively little yolk in them.
Stage 1 - crushing. This is the initial stage of embryonic development. Its main
meaning lies in the formation of multicellularity.
At this stage, the zygote first mitotically divides 2 times in the longitudinal direction.
Four identical cells are obtained - blastomeres. The blastomeres then divide
alternately in the transverse and longitudinal directions. Cell division is fast
Blastomeres do not grow, and their size decreases as the number of cells increases.
Cleavage ends with the formation of a spherical blastula (from the Greek blastos - germ,
sprout), the wall of which consists of a single layer of cells. Inside the blastula usually has
cavity. Starting from the blastula, the cells of the embryo are usually called not blastomeres, but
embryonic cells
2 - Stage of gastrulation
In the lancelet, like in all other multicellular animals, cleavage is followed by
stage of gastrulation. It is a complex process of moving
embryonic material with the formation of two and then three layers of the body of the embryo,
called germ layers (ectoderm, mesoderm, ectoderm).
During gastrulation, the embryo becomes two-layer due to invagination of the part
cells of the single-layer wall of the blastula. Germinal layers gradually separate
ectoderm (outer layer of cells) and endoderm (inner layer of cells) of the gastrula (from
Greek gaster - stomach). The cavity enclosed by the endoderm is called the cavity.
primary intestine. With further development of the gastrula, a third
the germ layer is the mesoderm. It is laid in the form of two pocket-shaped
protrusions of the endoderm and lies between the ectoderm and endoderm.
Neurula (in chordates) the stage of development of the embryo following the gastrula, on
which is laid from the ectoderm of the plate of the neural tube and axial organs.
3 Stage of histogenesis and organogenesis
The germ material differentiated into three germ layers gives rise to
all tissues and organs. The process of tissue formation is called histogenesis, and
organ formation - organogenesis.
During embryonic development from germ layers in multicellular animals
all organ systems of the whole organism arise.
From the ectoderm (outer germ layer) the organs of the nervous system are formed,
sensory organs and outer coverings of the body (epidermis). Mesoderm (middle germinal
leaf) gives rise to the skeleton, muscles, circulatory, urinary systems and
system of reproductive organs, as well as the dentin of the teeth and the dermis of the skin. From endoderm cells
(inner germ layer) the digestive system is formed (except
salivary glands), lungs and respiratory tract epithelium.
In animals, three types of ontogeny are distinguished: larval, ovipositor, and intrauterine.
The larval type of development is found, for example, in insects, fish, and amphibians.
There is little yolk in their eggs, and the zygote quickly develops into a larva, which
feeds and grows on its own. Then, after some time,
metamorphosis transformation of a larva into an adult. In some species, there is
even a whole chain of transformations from one larva to another and only then to an adult
individual. The meaning of the existence of larvae may lie in the fact that they feed on another
food than adults, and thus the food base of the species is expanding.
Compare, for example, the nutrition of caterpillars (leaves) and butterflies (nectar), or
tadpoles (zooplankton) and frogs (insects). Moreover, in the larval stage
many species actively colonize new territories. For example, the larvae of bivalves
mollusks are capable of swimming, and adults are practically motionless.
The oviparous type of ontogenesis is observed in reptiles, birds and oviparous
mammals whose eggs are rich in yolk. The embryo of these species develops
inside the egg; the larval stage is absent. Intrauterine type of ontogeny
observed in most mammals, including humans. Wherein
the developing embryo lingers in the mother's body, a temporary
the placenta, through which the mother's body provides all the needs of the growing
embryo: respiration, nutrition, excretion, etc. Intrauterine development ends
the process of childbearing.
The impact of environmental factors on the development of the embryo.
Study of the influence of environmental factors on the development of the human embryo.
1) The influence of alcohol on the development of the human fetus (a report is being heard)
It should not be imagined that alcohol defects are always so
It is obvious that by the appearance of the child you can immediately determine whether it is or not.
For example, microcephaly is an underdevelopment of the cerebral cortex that can manifest itself in
varying degrees: from a very moderate deviation from the norm to complete
absence of the cerebral cortex.
I will give the result of one of the many medical studies of the influence
alcohol on human development at different stages.
American researchers monitored the course of pregnancy
in 130 women and the subsequent development of children born. Thirteen of them, i.e. 10% off
of the entire group were drinkers, the rest did not drink alcohol. Otherwise
the conditions for the course of pregnancy were the same (proper nutrition,
movements, medical supervision).
It turned out that the development of all children born to women who use
alcoholic products, significantly deviated from the normal. They were all smaller
and birth weight, poorer development of the limbs, they grew more slowly, lagged behind in
motor activity, had more or less pronounced developmental defects such as
fetal alcohol syndrome.
Drinking mothers and grown-up daughters of once-drinking mothers are significantly more likely to
give birth to premature babies, their offspring are much more likely to have such
ailments like cerebral palsy and multiple sclerosis, very bad
treatable with current traditional medicine.
Careful comparative observations of subsequent years did not allow us to establish
not a single case of the birth of a completely normal child by a woman, systematically
drinking alcohol.
Conclusion: if you want health for your future children, do not drink. Too big a risk
unforeseen complications.
However, men should not drink either. Here are the observations of an experienced pediatrician,
V.A. Dulnev, who studied 64 children born from fathers for 45 years
regularly consumed alcohol. The results of the observations were
signs of mental retardation were found in all children without exception, even in those
who are well developed physically.
French doctors, analyzing the development of children whose fathers are of different times
abstained from the use of alcoholic products, came to a sufficient
optimistic conclusion that in order to produce full-fledged offspring, a man must
do not drink for 12 years (this also applies to women).
Remember: WHEN YOU DRINK, YOU DESTROY WHAT YOU DON'T OWN
health of YOUR children
2) The effect of nicotine on the development of the human fetus (a report is being heard)
Smoking of a pregnant woman causes: spasm of uterine vessels with slowing down
uteroplacental blood flow, lasting 20-30 minutes after one smoked
cigarettes; suppression of fetal respiratory movements; the appearance of nicotine in the blood of the fetus and
other toxic substances, which leads to growth retardation, body weight and birth
a child with its deficiency; there is a development of pulmonary pathology, as in a newborn,
as well as in older children; increased risk of perinatal mortality and
sudden death syndrome in the neonatal period is a rather mysterious phenomenon when
a child under the age of one year suddenly, for no apparent reason, dies.
Malformations caused by smoking.
Already in the late 60s - early 70s, doctors drew attention to the fact that
some craniofacial anomalies seem to be somewhat more common in children,
born to women who smoked during pregnancy. More accurate statistics
observations confirmed the reliability of this assumption: indeed, "wolf
mouth", that is, splitting of the hard palate, and "cleft lip", that is, splitting of the upper
lips, in newborns whose mothers smoked during pregnancy, is more common.
What is the mechanism for the occurrence of deformities under the influence of tobacco smoke?
is unknown, there are few special works on this issue: all the same, both the frequency and
the severity of this anomaly is not as significant as, say, in alcohol syndrome.
But the fact that smoking during pregnancy contributes to the birth of children with cranial
facial anomalies, no longer subject to doubt.
Statistical analysis of life expectancy of smokers and non-smokers
found that every cigarette smoked shortened life by five to six
minutes. But no one knows how much is reduced from each cigarette smoked
pregnant woman, the life of the unborn child. Such data simply cannot yet be
- 50-70 years ago there were very few women who smoked. But now, sadly,
the basis for such calculations is already being created.
But mental abnormalities in offspring do not have to wait long -
the consequences of nicotine exposure to the embryo and fetus appear quickly. And if
the child falls asleep badly, is often naughty, overly excited, then this is not necessary
from bad upbringing. Let the mother ask herself if she did not succumb to the temptation at least
occasionally smoke a cigarette (or drink a glass of wine) for nine months.
But let's not close our eyes to the fact that the need caused by this habit
requires constant gratification in order to experience pleasure or avoid
discomfort, and, most importantly, that relatively small stimulating or depressive
effect on the central nervous system (after all, smokers are drawn to a cigarette and when
want to cheer up, and when they want to calm down) cannot be compared with that
colossal harm caused by three thousand chemical compounds,
contained in tobacco smoke. The most essential thing is tobacco, like alcohol, bringing
dubious pleasure to parents, ruin their children.
The effect of drugs on the development of pregnancy
Long-term drug use leads to negative changes in
physical and mental health of people. Drug addicts suffer from disorders
digestion, damage and destruction of the liver occurs, cells actively die
the brain, the activity of the cardiovascular system is disrupted, etc. At
drug use, there is a significant decrease in the production of sexual
hormones (reduced ability to conceive). And although the sex drive in drug addiction
progressively decreases, about 25% of drug addicts have children. who suffer
various serious illnesses and pathologies caused by the use of drugs
parents. Some drugs provoke negative changes even in
chromosomes of germ cells, leading to chromosome breaks. Chromosomal abnormalities
always lead to adverse consequences for offspring. Majority
embryos with such developmental disorders die, but the living ones form
serious malformations - deformities. Newborn deaths in
women taking drugs reaches 80%.
The toxic effect of drugs on the fetus can be direct (through
damage to its cellular structures) and indirect (through a violation of the formation
hormones, changes in the lining of the uterus). Drugs have little
molecular weight and easily cross the placenta. Because the fetal liver
sufficiently developed drugs are slowly neutralized and circulate for a long time in its
body, bringing irreparable damage to the systems and organs of the developing
organism.
If a woman takes drugs during pregnancy, then with her
the child takes the drug. The mother is a drug addict, the child also becomes
drug addict, and after childbirth, such children often experience symptoms of the so-called
"withdrawal" that occurs when you refuse to take drugs and manifests itself in the form
severe irritability and nervous excitement).
Taking drugs during pregnancy leads to complications such as:
the risk of the birth of a dead fetus, miscarriage increases sharply, weight loss occurs
newborn, mental retardation, premature birth, and may also
develop sudden infant death syndrome (risk of sudden infant death syndrome when
opium consumption during pregnancy is twenty times higher.) Some drugs
(opium and cocaine), bringing not only direct harm to the development of the child, but also
indirectly, they lead to constriction of the blood vessels of the placenta, thereby
limiting the supply of oxygen to the fetus (like nicotine, cause oxygen
fetal starvation). By acting on the brain of a child, cocaine leads to its increased
irritability. Marijuana, the use of which during pregnancy was considered
safe for the child, has the same effect on the development of the fetus as other
drugs.
Pregnancy imposes a great responsibility on a woman. Now she needs
worry not only about the state of your health, but also about the health of your future
child. In the embryonic period, when the child is especially vulnerable, the use
drugs to have an irreparable negative impact not only on the psyche, but on everything
later development of the organism
Ontogenesis is the process of individual development of an individual from the moment a zygote is formed during sexual reproduction (or the appearance of a daughter individual during asexual reproduction) until the end of life.
The periodization of ontogeny is based on the possibility of sexual reproduction by an individual. According to this principle, ontogenesis is divided into three periods: pre-reproductive, reproductive and post-reproductive.
The pre-reproductive period is characterized by the inability of an individual to sexual reproduction, due to its immaturity. During this period, the main anatomical and physiological transformations take place, forming a sexually mature organism. In the pre-reproductive period, the individual is most vulnerable to the adverse effects of physical, chemical and biological environmental factors.
This period, in turn, is divided into 4 periods: embryonic, larval, metamorphosis period and juvenile.
The embryonic (embryonic) period lasts from the moment of fertilization of the egg to the release of the embryo from the egg membranes.
The larval period occurs in some representatives of the lower vertebrates, the embryos of which, having emerged from the egg membranes, exist for some time, not having all the features of a mature individual. The larva is characterized by the embryonic features of the individual, the presence of temporary auxiliary organs, the ability to actively feed and reproduce. Due to this, the larva completes its development in the most favorable conditions for this.
Metamorphosis as a period of ontogenesis is characterized by structural transformations of the individual. In this case, the auxiliary organs are destroyed, and the permanent organs are improved or newly formed.
The juvenile period lasts from the end of metamorphosis to the entry into the reproductive period. During this period, the individual grows intensively, the final formation of the structure and function of organs and systems occurs.
In the reproductive period, the individual realizes its ability to reproduce. During this period of development, it is finally formed and resistant to the action of adverse external factors.
The post-reproductive period is associated with progressive aging of the body. It is characterized by a decrease, and then the complete disappearance of the function of reproduction, reverse structural and functional changes in the organs and systems of the body. Reduced resistance to various adverse effects.
Postembryonic development can be direct or indirect. With direct (without a larva) development, an organism similar to an adult emerges from the egg membranes or from the mother's body. Postembryonic development of these animals is reduced mainly to growth and puberty. Direct development occurs in animals that breed by laying eggs when the eggs are rich in yolk (invertebrates, fish, reptiles, birds, some mammals), and in viviparous forms. In the latter case, the eggs are almost devoid of yolk. The embryo develops inside the mother's body, and its vital activity is provided by the placenta (placental mammals and humans).
Indirect development - larval, with metamorphosis. Metamorphosis can be incomplete, when the larva resembles an adult organism and becomes more and more similar to it with each new molt, and complete, when the larva differs from the adult organism in many of the most important features of the external and internal structure, and the pupa stage is present in the life cycle.
2. Embryonic development
The period of embryonic development is most complex in higher animals and consists of several stages.
The first stage of embryonic development is cleavage. At the same time, first 2 cells are formed from the zygote by mitotic division, then 4, 8, etc. The resulting cells are called blastomeres, and the embryo at this stage of development is called blastula. At the same time, the total mass and volume almost do not increase, and new cells become smaller and smaller. Mitotic divisions occur rapidly one after another, characterized by a shortening and sometimes by the loss of some stages of mitosis. Thus, this process is characterized by much faster DNA replication. Stage G1 (preparation for DNA synthesis and cell growth) falls out. Stage G2 is significantly shortened. This rapid succession of mitotic divisions is provided by the energy and nutrients of the cytoplasm of the egg.
Sometimes the resulting blastula is a cavity formation in which the blastomeres are arranged in one layer, limiting the cavity - the blastocoel. In cases where the blastula looks like a dense ball without a cavity in the center, it is called a morula (morum - mulberry).
The next stage of embryonic development is gastrulation. At this time, blastomeres, which continue to divide rapidly, acquire motor activity and move relative to each other, forming layers of cells - germ layers. Gastrulation can occur either by invagination (invagination) of one of the walls of the blastula into the cavity of the blastocoel, immigration of individual cells, epiboly (fouling), or delamination (splitting into two plates). As a result, the outer germ layer is formed - the ectoderm, and the inner one - the endoderm. In most multicellular animals (except for sponges and coelenterates), a third, middle germ layer, the mesoderm, is formed between them, formed from cells lying on the border between the outer and inner sheets. Then comes the stage of histo- and organogenesis. At the same time, the rudiment of the nervous system, the neurula, is first formed. This occurs by isolating a group of ectoderm cells on the dorsal side of the embryo in the form of a plate, which folds into a groove, and then into a long tube and goes deep into, under the layer of ectoderm cells. After that, the rudiment of the brain and sense organs is formed on the front of the tube, and the rudiment of the spinal cord and peripheral nervous system is formed from the main part of the tube. In addition, the skin and its derivatives develop from the ectoderm. The endoderm gives rise to the organs of the respiratory and digestive systems. Muscle, cartilaginous and bone tissue, organs of the circulatory and excretory systems are formed from the mesoderm.
Preparation for ZNO. Biology.
Synopsis 39. Ontogeny. Life cycle
Ontogenesis- the individual development of an individual, the totality of its interrelated transformations, naturally occurring in the process of implementing the life cycle from the moment of formation of a zygote to death.
In multicellular animals that reproduce sexually, ontogeny is divided into periods:
1. embryonic(from the formation of a zygote to birth or exit from the egg membranes),
2. postembryonic(from the exit from the egg membranes or birth to the death of the organism) periods.
Gametes or sex cells- haploid cells that are formed in the gonads and form a zygote upon fusion.
Gametogenesis the process of development of gametes. The process of sperm formation is called spermatogenesis and the formation of oocytes ovogenesis.
Embryonic period
Splitting up- This is a series of successive mitotic divisions of the zygote, as a result of which the huge volume of the cytoplasm of the egg is divided into numerous smaller cells containing nuclei. As a result of crushing, cells are formed, which are called blastomeres. It differs from ordinary division in that the newly formed blastomeres do not increase in size. It ends with the formation of the blastula.
Blastula- single-layer embryo. Consists of a layer of cells blastoderm, limiting the cavity - blastocoel. Blastula begins to form in the early stages of cleavage due to the divergence of blastomeres. The resulting cavity is filled with liquid.
gastrulation- the formation of germ layers in the blastula. As a result of gastrulation, a two-layer, and then a three-layer embryo is formed (in most animals) - gastrula. Initially, the outer ( ectoderm) and internal ( endoderm) layers. Later, between the ecto- and endoderm, a third germ layer is laid - mesoderm.
germ layers- separate layers of cells that occupy a certain position in the embryo and give rise to the corresponding organs and organ systems. The germ layers arise not only as a result of the movement of cell masses, but also as a result of the differentiation of similar, relatively homogeneous blastula cells.
Differentiation- the process of the appearance and growth of morphological and functional differences between individual cells and parts of the embryo. Depending on the type of blastula and on the characteristics of cell movement, the following main methods of gastrulation are distinguished: invagination, immigration, delamination, epiboly.
Immigration– “violation” of part of the blastoderm cells into the cavity of the blastocoel (higher vertebrates). These cells form the endoderm.
Delamination occurs in animals that have a blastula without a blastocoel (birds). With this method of gastrulation, cell movements are minimal or completely absent, since stratification occurs - the outer cells of the blastula are transformed into the ectoderm, and the inner cells form the endoderm.
epiboly occurs when the smaller blastomeres of the animal pole cleave faster and grow over the larger blastomeres of the vegetative pole, forming the ectoderm (amphibians). The cells of the vegetative pole give rise to the inner germ layer - the endoderm.
With the formation of the mesoderm, the formation of a secondary body cavity occurs, or coelom.
Organogenesis- the process of formation of organs in embryonic development.
There are two phases:
1. neurulation- formation of a complex of axial organs (neural tube, notochord, intestinal tube and somite mesoderm), which involves almost the entire embryo;
2. construction of other organs, the acquisition by various parts of the body of their typical form and features of internal organization, the establishment of certain proportions (spatially limited processes).
Neirula- an embryo at the stage of neurulation. The material used to build the nervous system in vertebrates, the neuroectoderm, is part of the dorsal part of the ectoderm. It is located above the rudiment of the chord.
The germ layer theory of Karl Baer: the appearance of organs is due to the transformation of one or another germ layer - ecto-, meso- or endoderm. Some organs may be of mixed origin, that is, they are formed with the participation of several germ layers at once. For example, the musculature of the digestive tract is a derivative of the mesoderm, and its inner lining is a derivative of the endoderm.
Embryonic induction- this is the interaction between the parts of the embryo, during which one part of it - the inductor - in contact with another part - the reacting system - determines the direction of development of the latter.
Postembryonic period of development
Postembryonic period development begins at the moment of birth or release of the organism from the egg membranes and continues until its death.
There are two main types of postembryonic development:
1. straight;
2. with transformation.
Life cycle- a regular change of all generations (ontogenies) characteristic of a given type of living organisms. One should clearly distinguish ontogeny(s) of the life cycle (characteristics of the species) from ontogeny (development of an individual from the moment of its appearance to the moment of death or division).
By the number of generations (ontogenies) in the life cycle:
1. Simple: cycle includes one generation.
2. Complex: the cycle includes two or more generations; such a life cycle is typical, for example, for many coelenterates (alternation of generations of polyps and jellyfish), for most trematodes (alternation of generations of marites, sporocysts and redia).
Regeneration- the ability of living organisms to restore damaged tissues over time, and sometimes entire lost organs. Regeneration is also called the restoration of a whole organism from its artificially separated fragment (for example, the restoration of a hydra from a small fragment of the body or dissociated cells). In protists, regeneration can manifest itself in the restoration of lost organelles or cell parts.
