Reviewing SCERT Class 8 Basic Science Solutions and Kerala Syllabus Class 8 Basic Science Chapter 18 Cells that Become Daughter Cells Question Answer Notes Pdf can uncover gaps in understanding.
Class 8 Basic Science Chapter 18 Cells that Become Daughter Cells Question Answer Notes
Class 8 Basic Science Chapter 18 Notes Kerala Syllabus Cells that Become Daughter Cells Question Answer
Cells that Become Daughter Cells Class 8 Questions and Answers Notes
Let’s Assess
Question 1.
Complete the table by selecting the appropriate human reproductive organs and associated parts from the box.
Answer:
| Details | Male reproductive system | Female reproductive system |
| 1. Function | 1. Produces sperm and sex hormones | 5. Produces eggs and female sex hormones |
| 2. Important parts | 2. Testes, scrotum, penis | 6. Ovary, fallopian tube, uterus, vagina |
| 3. Where gamete production occurs | 3. In the testes | 4. In the ovary |
Question 2.
Find the incorrect statements given below and rewrite them correctly.
a) The number of chromosomes in germ cells is 46.
b) The number of chromosomes in a human zygote is 92.
c) Budding is an example of asexual reproduction.
d) Four eggs are produced from a single germ cell of an ovary.
Answer:
a) Correct. (Germ cells in the reproductive organs, before meiosis, are diploid and have 46 chromosomes).
b) Incorrect.
Correction: The number of chromosomes in a human zygote is 46. (It is formed by the fusion of a sperm with 23 chromosomes and an egg with 23 chromosomes).
c) Correct. (As seen in Yeast).
d) Incorrect.
Correction: One egg (ovum) and three polar bodies are produced from a single germ cell of an ovary during meiosis.
Question 3.
Complete the flowchart and give an appropriate title.
Answer:
Basic Science Class 8 Chapter 18 Question Answer Kerala Syllabus
Textbook Page No : 288
Question 1.
Analyse the illustration and completethe given Table 18.1.?
Answer:
| Number | Modes of reproduction | Examples |
| 1 | New plants grow from the leaf (Vegetative propagation from leaf) | Bryophyllum Sansevieria |
| 2 | New plants grow from the root | Curry leaf plant |
| 3 | New plants grow from the stem (Vegetative propagation from stem cutting) | Tapioca, Rose, Hibiscus, Sugarcane |
| 4 | Under favourable conditions, the cell divides and becomes two organisms. | Amoeba, Paramecium, Euglena |
| 5 | In unfavourable conditions, cells in organisms like plasmodium develop a thick outer covering.The cytoplasm and nuclear materials inside the cell divide into several parts. When the conditions become favourable, the outer covering of the cell breaks, open, releasing many tiny cells, each of which grows into a new organism. | Plasmodium |
| 6 | Regeneration: Body parts break off and regenerate into new organisms. | Planaria, Hydra |
| 7 | Budding: A small outgrowth (bud) forms on the parent cell, develops, and separates to form a new organism. | Yeast |
Textbook Page No : 289
Question 2.
What is the fundamental difference between the reproductive methods we have discussed so far and the method of reproduction shown in the illustration below?
Answer:
Illustration 18.1 shows plants growing from seeds. This method is fundamentally different from the asexual methods discussed above because it involves the formation of seeds through sexual reproduction.
Question 3.
Observe the structure of flowers, which are the reproductive organs of plants and complete the illustration 18.2.
Answer:
Textbook Page No : 290
Question 4.
How do pollen grains from the anther reach the stigma?
Answer:
The process by which pollen grains are transferred from the anther (male part) to the stigma (female part) is called pollination. Since pollen grains cannot move on their own, they rely on external “agents” to carry them. Animals like insects and birds as well as wind and water, help in pollination
Question 5.
What happens to the pollen grain after pollination?
Answer:
After pollination, the pollen grain starts a journey to fertilize the egg inside the ovary. This process is called fertilization.
Question 6.
Shall we try a simple experiment with the help of the teacher? Prepare a note with diagram based on the experiment you conducted. [Illustration 18.3]
Answer:
Collect mature pollen grains from a flower’s anther.
Place them on a slide with a drop or two of sugar solution.
Observe under a microscope after 3 – 4 hours.
Observation: The pollen tube grows from the deposited pollen grain down towards the ovary. This tube carries the male gametes to fertilize the ovule inside the ovary.
Textbook Page No : 292
Indicators
Question 7.
Function of the tube nucleus …………………
Answer:
Controls the formation and growth of the pollen tube, then disintegrates.
Question 8.
Function of the pollen tube
Answer:
The pollen tube grows down through the style and enters the ovule, transporting the two male gametes into the ovary.
Question 9.
Formation of male gametes
Answer:
Generative nucleus divides to form two male gametes
Question 10.
Fertilization
Answer:
One of the male gametes that reaches the ovule through the pollen tube fuses with the egg cell to form a zygote. This process is known as fertilization.
Question 11.
Formation of endosperm
Answer:
The zygote grows and becomes an embryo. The embryo then grows into a seedling. The second male gamete fuses with the polar nuclei to form the endosperm. The endosperm stores the food needed for the growth of the embryo.
Textbook Page No : 294
Question 12.
Parts and functions of the reproductive system in human being.
Answer:
| Parts | Functions |
| Male reproductive System | |
| Vas Deferens | Transports male gametes from the testes to the urethra. |
| Prostate gland | It produces a fluid that contains the substances needed for the nourishment and movement of the sperms. |
| Testis | It produce sperm and male sex hormones (testosterone) |
| Penis | Through this duct, both urine and sperm are discharged. It helps to deliver the sperm into the vagina. |
| Female reproductive system | |
| Uterus | The part that completes the growth of the embryo |
| Fallopian tube | It carries the ovum to the uterus. Fertilization takes place here. |
| Ovary | Ovary produces the ovum and female sex hormones, estrogen and progesterone. |
| Vagina | The part that opens the uterus to the outside. It is where the semen is deposited. During childbirth, the baby comes out through this part. |
| The part that completes the growth of the embryo | |
Question 13.
Production of gametes
Answer:
Testis produces sperm in male. Ovary produces the ovum in females.
Question 14.
Sexual hormones
Answer:
Testis produces male sex hormones (testosterone). Ovary produces the female sex hormones, estrogen and progesterone.
Textbook Page No : 295
Question 15.
Complete the table 18.2
Answer:
| Characteristics | Sperm | Ovum |
| Shape | Head, body, and tail | Spherical |
| Size | Smaller | Larger |
| Motility | Motile (using tail) | Non-motile |
Textbook Page No : 297
Indicators
Question 16.
Site of fertilization.
Answer:
Fallopian Tube (specifically the ampulla region). This is where the sperm meets and fuses with the egg.
Question 17.
Embryo formation.
Answer:
Uterus (Womb). The fertilized egg divides to form an embryo while traveling, but it implants and develops into a baby in the wall of the uterus.
Question 18.
Menstruation.
Answer:
Uterus.Menstruation is the shedding of the inner lining of the uterus (endometrium), which flows out through the vagina.
Textbook Page No : 298
Let’s Find
Question 19.
What happens when cell division occurs in unicellular organisms?
Answer:
When a unicellular organism divides, it is reproducing, creating exact copies of itself, and the original parent cell ceases to exist as a single entity.
Textbook Page No : 299
Question 20.
Formation of chromosomes.
Answer:
Occurs during Prophase as the chromatin network condenses.
Question 21.
Stages of cell division
Answer:
Prophase, Metaphase, Anaphase, Telophase.
Question 22.
Number of chromosomes in the parent cell and daughter nuclei.
Answer:
The number of chromosomes in the daughter nuclei is the same as the number in the parent cell, (e.g., If the parent human cell had 46 chromosomes, each daughter nucleus will also have 46 chromosomes). Karyokinesis maintains the chromosome number.
Question 23.
Number of daughter nuclei formed in one division.
Answer:
Two daughter nuclei are formed in one division.
Textbook Page No : 301
Question 24.
Complete the illustration 18.13.
Answer:
Textbook Page No : 303
Indicators
Question 25.
Number of chromosomes in human germ cells
Answer:
23 chromosomes.
Germ cells (sperm and egg) are haploid (n). This is exactly half the number found in normal body cells (which have 46).
Question 26.
Characteristic of Meiosis Stage I
Answer:
It is a Reductional Division. The homologous chromosome pairs separate. This reduces the chromosome number by half (e.g., from 46 to 23), which is why the resulting cells are haploid.
Question 27.
Similarity between Meiosis Stage II and Mitosis
Answer:
Both involve the separation of sister chromatids. In both processes, the centromeres split and the individual chromatids are pulled to opposite poles. Because the chromosome number does not drop further, both are considered “equational divisions.”
Question 28.
Difference observed in the process of gamete formation in males and females
Answer:
The process is called Spermatogenesis in males and Oogenesis in females.
| Spermatogenesis | Oogenesis |
| The cytoplasm is shared equally among daughter cells. | Most cytoplasm goes to one big egg; the others become tiny “polar bodies.” |
| One parent cell produces 4 active sperm. | One parent cell produces only 1 active egg. |
| Starts at puberty and is continuous. | Starts before birth (fetus stage), pauses, and resumes at puberty. |
Question 29.
Complete the table 18.3.
Answer:
| Details | Mitosis | Meiosis |
| In which cells does it occur? | In the normal cells of the body | In the germinal cells of the reproductive organs |
| Changes in chromosome number | No change (Remains the same) | Reduced to half |
| Number of daughter cells | 2 | 4 |
| Significance | Helps in the growth of the body and repair of tissues. | Germ cells are formed. In organisms that undergo sexual reproduction helps to maintain a constant number of chromosomes across generations. |
Textbook Page No : 305
Question 30.
Complete the table 18.4.
Answer:
| Details | Fraternal twins | Identical twins | Siamese twins |
| Formation method | Two eggs fertilized by two different sperm. | Single zygote divides completely into two. | Incomplete division of zygote OR fusion of separated cells. |
| Structural similarity | Will not be the same. | Will be the same. | Will be the same; bodies are joined. |
| Hereditary factors | Will not be the same. | Will be the same. | Will be the same. |
| Sexual characteristics | May be the same or different gender. | Will always be the same sex. | Will always be the same sex. |
Textbook Page No : 305
Question 31.
Analyse illustrations 18.16, 18.17, and their descriptions, and write down your conclusions.
Answer:
Humans grow through distinct stages from birth to o|d age, including infancy, childhood, adolescence, adulthood, and old age. A particularly significant stage is adolescence. Adolescence (known as Kaurmaram in Malayalam) is the transitional phase leading from childhood to full maturity, generally spanning from ages 10 to 19. This period is characterized by rapid physical, mental, and emotional changes. Physically, individuals experience a growth spurt with a sudden increase in height and weight, alongside accelerated growth of the reproductive organs and increased activity of glands in the skin. Simultaneous with these physical changes, the brain continues to develop, resulting in significant shifts in thinking, emotions, and social interactions. It is also observed that the parts of the brain controlling these changes develop earlier in girls, leading to faster growth during puberty compared to boys.
Class 8 Basic Science Chapter 18 Question Answer Extended Activities
Question 1.
Prepare suitable questions about the human reproductive system and sexual hygiene, conduct an interview with a doctor and prepare a report.
Question 2.
Prepare a chart/slide presentation about diseases related to the reproductive organs.
Cells that Become Daughter Cells Class 8 Notes
Class 8 Basic Science Cells that Become Daughter Cells Notes Kerala Syllabus
Reproduction
- The biological process of producing new individual organisms (offspring), ensuring the continuation of a species.
- Types:
- Asexual Reproduction: From a single parent, offspring are genetically identical (e.g., Binary Fission, Budding, Regeneration, Spore Formation, Vegetative Propagation).
- Sexual Reproduction: Involves the fusion of male and female gametes (formed by meiosis) through fertilization to form a zygote. Offspring are genetically diverse.
ഒരു ജീവിയിൽ നിന്ന് പുതിയ തലമുറ ഉണ്ടാകുന്ന പ്രക്രിയയാണ് പ്രത്യുത്പാദനം. ഇത് വർഗ്ഗത്തിന്റെ (species) തുടർച്ച ഉറപ്പാക്കുന്നു. ഒരൊറ്റ ജീവിയിൽ നിന്ന് പുതിയ ജീവികളു ണ്ടാകുന്ന രീതിയാണ് അലൈംഗിക പ്രത്യുത്പാദ നം (Asexual Reproduction). ഉദാഹരണങ്ങൾ: ഇലമുളച്ചിയിൽ ഇലയിൽ നിന്നും, കപ്പയിൽ തണ്ടിൽ നിന്നും പുതിയ ചെടികളുണ്ടാകുന്നത് (കായിക പ്രജനനം / Vegetative Propagation); ബാക്ടീരിയ രണ്ടായി വിഭജിക്കുന്നത് (Binary Fission); പ്ലാനേറിയ മുറിഞ്ഞ ഭാഗങ്ങളിൽ നിന്ന് വളരുന്നത് (Regeneration); യീസ്റ്റിൽ മുകുള ങ്ങൾ ഉണ്ടാകുന്നത് (Budding).
Sexual Reproduction in Plants: Seeds
□ Plants growing from seeds. This method is fundamentally different from the asexual methods discussed above because it involves the formation of seeds through sexual reproduction.
Structure of a Flower
Main Parts:
- Petals (ദളങ്ങൾ): Often brightly coloured to attract pollinators.
- Sepals (വിതളങ്ങൾ): Usually green, leaf-like structures that protect the bud.
- Pedicel (പൂഞ്ഞട്ട്): The stalk of the flower.
- Thalamus: The part of the stalk where the floral organs are attached.
Reproductive Organs:
- Stamen (കേസരം): The Male reproductive organ.
- Anther (പരാഗി): The part that produces pollen grains.
- Filament: The stalk that holds the anther.
- Pistil / Carpel: The Female reproductive organ.
- Stigma: The receptive tip where pollen lands.
- Style: The stalk connecting the stigma to the ovary.
- Ovary: Contains the ovules, which develop into seeds after fertilization.
Pollination
Pollen grains containing the male gametes are formed in the anther (part of the stamen). The process of these pollen grains settling on the stigma (part of the pistil) is called pollination.
- Pollinating Agents: Animals like insects and birds, as well as wind and water, help in pollination.
- The polien tube grows from the deposited pollen grain down towards the ovary. This tube carries the male gametes to fertilize the ovule inside the ovary.
- After pollination, the pollen grain germinates on the stigma and the pollen tube grows towards the ovule inside the ovary.
Fertilization
One of the male gametes that reaches the ovule through the pollen tube fuses with the egg cell to form a zygote. This process is known as fertilization.
- The zygote grows and becomes an embryo. The embryo then grows into a seedling.
- The second male gamete fuses with the polar nuclei to form the endosperm. The endosperm stores the food needed for the growth of the embryo.
Endosperm vs. Cotyledons:
- In monocot plants (like paddy, maize, coconut), the endosperm itself is the primary stored food used during germination, and it’s often the edible part.
- In dicot plants, the food required for the embryo is stored in the cotyledon.
പരാഗണത്തിനുശേഷം (Pollination) പരാഗരേണു (pollen grain) മുളച്ച് പരാഗനാളി (pollen tube) അണ്ഡാശയത്തിലെ (Ovary) അണ്ഡത്തിലേക്ക് (Ovule) വളരുന്നു. പരാഗനാളിയിലൂടെ എത്തുന്ന രണ്ട് പുരുഷബീജങ്ങളിൽ (male gametes) ഒന്ന് അണ്ഡവുമായി (Ovum) ചേർന്ന് സിക്താണ്ഡം (Zygote) ഉണ്ടാകുന്നു. ഇതാണ് ബീജസങ്കലനം (Fertilization). സിക്താണ്ഡം വളർന്ന് ഭ്രൂണം (Embryo) ആകുന്നു. രണ്ടാമത്തെ പുരുഷബീജം അണ്ഡത്തിലെ പോളാർ ന്യൂക്ലിയസുമായി ചേർന്ന് എൻഡോസ്പേം (Endosperm) ഉണ്ടാകുന്നു. എൻഡോസ്പേം ആണ് ഭ്രൂണത്തിന്റെ വളർച്ചക്കാവ ശ്യമായ ആഹാരം സംഭരിക്കുന്നത്.
Fertilization
Like plants, animals also have specialized organ systems for reproduction. Reproduction in humans is sexual reproduction.
Hormones: Chemical substances produced by endocrine glands that control and coordinate various life activities, including reproduction.
Male reproductive System
In males, the testes are located in the scrotal sac just below the penis. For sperm production, a temperature 2 to 2.5 degrees Celsius lower than the normal body temperature is to be maintained. The contraction and relaxation of the scrotal sac helps in maintaining this temperature.
Female reproductive System
Gametes in Human Beings
Fertilization in Human Beings
- Semen: A combination of sperm cells formed in the testes and secretions from glands like the prostate.
- Ejaculation: The process by which semen is expelled through the penis.
- Sperm Transport: Sperm cells reach the vagina, pass through the uterus, and enter the fallopian tube.
- Fertilization: In the fallopian tube, one sperm unites with the egg (ovum) that has arrived there from the ovary. The process of the sperm uniting with the egg is called fertilization.
- Zygote Formation: Fertilization results in the formation of a zygote.
- Embryo Development: The zygote begins to divide and develops into an embryo. The embryo travels to the uterus and implants in the uterine wall (endometrium) to continue its growth.
പുരുഷബീജവും (Sperm) അണ്ഡവും (Ovum) സംയോജിക്കുന്ന പ്രക്രിയയാണ് ബീജസങ്കലനം (Fertilization). ഇത് സാധാരണയായി അണ്ഡവാ ഹിയിൽ (Fallopian tube) വെച്ചാണ് നടക്കുന്നത്. ബീജസങ്കലനത്തിന്റെ ഫലമായി സിക്താണ്ഡം (Zygote) രൂപപ്പെടുന്നു, അത് പിന്നീട് വളർന്ന് ഭ്രൂണമായി (Embryo) മാറുന്നു.
Ovulation & Menstruation
Illustration shows what happens after the ovary releases an egg.
- Ovulation: The process in which a fully matured ovum is released from the ovary.
- Preparation for Pregnancy: Along with ovulation, the thickness of the endometrium (inner lining of the uterus) increases, and more tissues and blood capillaries are formed in it, preparing to receive a fertilized egg.
Two Possibilities After Ovulation:
1. If Fertilization Occurs:
- A zygote is formed in the fallopian tube.
- The zygote develops into an embryo.
- The embryo implants in the thickened endometrium of the uterus and continues to grow. Pregnancy begins.
2. If Fertilization Does Not Occur:
- The released ovum disintegrates.
- The thickened endometrium (newly formed tissues and blood capillaries) is no longer needed.
- These tissues break down and are discharged through the vagina along with blood and mucus. This process is called Menstruation.
അണ്ഡാശയത്തിൽ നിന്ന് പൂർണ്ണവളർച്ചയെത്തിയ അണ്ഡം (Ovum) പുറത്തുവരുന്ന പ്രക്രിയയാണ് അണ്ഡവിസർജനം (Ovulation). ഇതോടൊപ്പം ഗർഭാശയത്തിന്റെ (Uterus) ആന്തരഭിത്തിയായ എൻഡോമെട്രിയം (Endometrium) കട്ടിയുള്ളതാ യി മാറുന്നു. ബീജസങ്കലനം (Fertilization) നടന്നാൽ, ഉണ്ടാകുന്ന ഭ്രൂണം (Embryo) ഈ ഭിത്തി യിൽ പറ്റിപ്പിടിച്ച് വളരും. ബീജസങ്കലനം നടന്നില്ലെ ങ്കിൽ, അണ്ഡം നശിച്ചുപോകുകയും, കട്ടിയുള്ള എൻഡോമെട്രിയം പാളി രക്തത്തോടൊപ്പം യോനി യിലൂടെ (Vagina) പുറന്തള്ളപ്പെടുകയും ചെയ്യുന്നു. ഇതാണ് ആർത്തവം (Menstruation).
Growth & Reproduction
Growth: From zygote to organism involves Cell Division, Cell Growth, and Cell Differentiation.
Cell Division Types:
1. Mitosis: For growth, repair, asexual reproduction. Produces two identical daughter cells with the same chromosome number as the parent. Stages: Prophase, Metaphase, Anaphase, Telophase. Cytokinesis differs in plant (cell plate) and animal (furrowing) cells.
- Mitosis takes place in two stages:
- Karyokinesis (division of the nucleus)
- Cytokinesis (division of the cytoplasm)
Karyokinesis: Each organism has a specific number of chromosomes. In human cells, the chromosome number is 46.
2. Meiosis: For gamete formation in sexual reproduction. Produces four daughter cells with half the chromosome number of the parent germ cell (e.g,, 46 → 23). In females, produces 1 ovum + 3 polar bodies. Maintains constant chromosome number across generations.
ശരീര വളർച്ചയ്ക്കും കേടുപാടുകൾ തീർക്കുന്നതി നും സഹായിക്കുന്ന കോശവിഭജനമാണ് ക്രമഭംഗം (Mitosis). ഇതിൽ ക്രോമസോം സംഖ്യയ്ക്ക് മാറ്റം വരുന്നില്ല. എന്നാൽ ലൈംഗിക പ്രത്യുത് പാദനത്തിനാവശ്യമായ ബീജകോശങ്ങൾ (Gametes) രൂപപ്പെടുന്നത് ഊനഭംഗം (Meiosis) വഴി യാണ്. ഇതിൽ ക്രോമസോം സംഖ്യ പകുതിയായി കുറയുന്നു (ഉദാ: 46 → 23).
Twins
- Identical Twins: Single zygote splits into two; genetically identical, same sex.
- Fraternal Twins: Two separate eggs fertilized by two different sperm; genetically like siblings, can be different sexes.
- Conjoined Twins: Incomplete splitting of a zygote; bodies joined, genetically identical, same sex.
Adolescence
- Age: ~10 to 19 years; transition from childhood to maturity.
- Changes: Growth spurt, reproductive organ growth, brain development, skin changes (acne due to sebum), mental/ emotional changes.
- Puberty: Physical changes for reproductive capability.
- Health: Importance of balanced nutrition, avoiding harmful influences (drugs, abuse), wise use of media.