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Metal and non metal

Posted on Monday, November 25, 2024

          Unit 17          

Metal and non metals


Exercise

1. Choose the correct option for the following questions:

a. Which is the main ore of iron?
iii) Hematite

b. Which metal is found in pure state in nature?
iv) Gold

c. Which is the primary step of purifying metal?
iii) Concentration

d. Which of the following ore is oxidised by roasting method?
i) hematite
ii) SIDERITE (Except siderite all are oxide ores here, and roasting is done for non oxide ore)
iii) bauxite
iv) Cuprite

e. In which process is smelting included?
iv) Reduction

2. Give reason:

a. All ores are minerals, but all minerals are not ores.
The mineral from which a metal can be extracted in a large amount with low cost is called the ore of that metal. The mineral from which a metal cannot be taken out easily are not the ores. Thus all ores are minerals but all minerals are not ores. For example, hematite is an ore of iron, while quartz is a mineral but not an ore.

b. Ores are oxidized after concentration.
Ores are oxidized after concentration because it is easier to obtain metals from their oxides.

3. Write the differences between:

a. Mineral and Ore
Minerals Ores
1. A mineral is a naturally occurring substance found in the earth's crust. 1. An ore is a type of rock that contains sufficient minerals to extract a metal profitably.
2. Minerals may or may not contain valuable metals. 2. Ores contain a high concentration of metal, making them valuable for extraction.
3. Minerals are the source of raw materials, and they are used for various industrial processes. 3. Ores are specifically mined to extract valuable metals or minerals.
4. Examples: Quartz, Mica, Feldspar, etc. 4. Examples: Bauxite (for aluminum), Hematite (for iron), Galena (for lead), etc.
5. All ores are minerals, but not all minerals are ores. 5. Ores are a subset of minerals that are economically viable to extract.


b. Roasting and Calcination
Roasting Calcination
1. Roasting is a process in which ore is heated in the presence of air (oxygen) at high temperatures. 1. Calcination is a process in which ore is heated in the absence of air (or limited air) at high temperatures.
2. It is used to extract metal oxides from sulfide ores by converting them into oxides. 2. It is used to remove volatile substances (such as water) or carbon dioxide from carbonates or other ores.
3. Roasting involves the chemical reaction between the ore and oxygen. 3. Calcination mainly involves thermal decomposition of ores.
4. The process of roasting can produce gases like sulfur dioxide (SO₂), which requires proper ventilation. 4. Calcination does not usually produce gases like sulfur dioxide but may release carbon dioxide (CO₂) when dealing with carbonates.
5. Example: Roasting of copper pyrite (CuFeS₂) to get copper oxide (CuO). 5. Example: Calcination of limestone (CaCO₃) to produce quicklime (CaO) and carbon dioxide (CO₂).


c. Oxidation and Reduction
Oxidation Reduction
1. Oxidation is the process in which an element loses electrons. 1. Reduction is the process in which an element gains electrons.
2. Oxidation involves an increase in the oxidation state of an element. 2. Reduction involves a decrease in the oxidation state of an element.
3. It often involves the addition of oxygen to a substance. 3. It often involves the removal of oxygen from a substance.
4. Oxidation results in the formation of oxides or other compounds where oxygen is added. 4. Reduction results in the formation of the pure element or a compound with fewer oxygen atoms.
5. Example: Oxidation of iron to form rust (Fe + O₂ → Fe₂O₃). 5. Example: Reduction of copper(II) oxide to copper (CuO + H₂ → Cu + H₂O).


4. Answer the following questions:

a. What are the sources of metals?
→ Minerals are sources of metals.

b. Make a list of ores of iron, copper, aluminium, and silver.
→ Iron: Hematite (Fe₂O₃), Magnetite (Fe₃O₄), Siderite (FeCO3), Limonite (2Fe2O3.3H2O), Iron Pyrite ( FeS2)

Copper: Chalcopyrite (CuFeS₂), Cuprite (Cu₂O), Chalcocite (Cu2S), Malachite [Cu2(OH)2CO3]

Aluminium: Bauxite (2Al₂O₃·2H₂O), Cryolite (Na3AlF6), Corundum (Al2O3)

Silver: Argentite (Ag₂S), Horn silver (AgCl), Ruby silver (Ag2Sb2S3), Silver copper glance [Ag(Cu)2S]

c. How is metallurgy a stepwise process? Explain.

→ Metallurgy involves the following steps:

Grinding: Crushing ores into small particles form with help of rollers.
Concentration: Removal of impurities (gangue) from ore.
Oxidation: Roasting or calcination to convert ores into oxides.
Reduction: Extraction of metals from their oxides using reducing agents like carbon or electrolysis.
Refining: Purification of extracted metals by methods such as electro-refining or distillation.
Hence, we can say metallurgy is stepwise process.

d. How are pure metals obtained from electro-refining? Explain it with an activity.
→ Following activity can be done to explain electro-refining process to obtain pure metals:

Materials Required: Copper sulfate solution, pure copper plate, impure copper, battery, voltameter and connecting wires.

Procedure:
- Take copper sulfate solution in voltameter
- Connect impure copper to the positive terminal of battery and pure copper to negative terminal of battery.
- Immerse both strips in the copper sulfate solution.

Observation: Impure copper plate in anode erodes and Pure copper getting deposited on the cathode.

Conclusion: In this way, we can get pure copper (Metals) from its impure form.

REVIEW OF THE CHAPTER

  • Metals are generally hard lustrous and good conductor of heat and electricity.
  • The elements and compounds which are naturally found on earth’s surface are called minerals.
  • The mineral from which a metal can be extracted in a large amount with low cost is called ore of that metal.
  • The unwanted earthy impurities present in the ores are called gangue or matrix.
  • The elements or chemicals used to remove gangue or matrix in ores are called flux.
  • The fusible mass obtained from chemical reaction between slag and flux is called slag.
  • Metallurgy is the science which deals about the properties, production and purification of metals. Metallurgy can be classified into Pyro metallurgy, electrometallurgy and hydrometallurgy.
  • The process of extracting useful substances and minerals from the earths geological surface is called mining.
  • Calcination is the process of in which ores are heated in absence of air or limited supply of air.
  • Roasting is the process in which ores are heated with excess supply of air.
  • Reduction is the process of removing oxygen from metal oxide by treating them with reducing agents like carbon, CO, hydrogen etc.
  • Smelting is the process of heating metals beyond their melting points along with a reducing agent.
  • The process of removing impurities present in metals obtained from reduction process by boiling is called distillation.
  • Electro-refining is the process of removing impurities present in metals obtained from reduction process by electrolysis.

Questions Asked in SEE


1. Which metal can be obtained from Argentite ore? [SEE 2080 Koshi]

i. Copper

ii. Gold

iii. Iron

iv. SILVER

2. What type of ore is concentrated by froth floatation process? [SEE 2080 Koshi]

→ Sulphide ore is concentrated by froth floatation process.

3. Write a main ore of copper. [SEE 2079 Koshi]

→ The main ore of copper is chalcopyrite.

4. A person is preparing a light and rust free toy. Among the metals iron, copper and aluminum available in market, which metal should he chose and why? [SEE 2079 Koshi]

→ He should chose aluminum because aluminum naturally forms a layer of aluminum oxide thus preventing from rusting. It is also lightweight, highly recyclable and cheap.

5. Define ore and mineral. [SEE 2080 Madhesh]

→ The mineral from which a metal can be extracted in a large amount with low cost is called ore of that metal.

→ The elements and compounds which are naturally found on earth’s surface are called minerals.



6. Suppose silver is being purified by electro refining method. Draw the figure of correct connection of materials with all requirements. [SEE 2080 Bagmati, Lumbini]

→


7. If we have to do following task during extraction of metal from its ore, which procedure can be used? [SEE 2080 Karnali]

i) To change ore into metallic oxide

→ Oxidation

ii) To separate hydrophilic and hydrophobic substances from ore

→ Froth floatation process

8. A gold ring was lost in field. When the ring was found after two months, it was found no change in its weight, why? [SEE 2080 Sudurpaschim]

→ There was no change in weight of gold ring even after two months because gold is less reactive element making it highly resistant to environmental degradation.

9. Show the labelled diagram for the purification of gold by electro refining process. [SEE 2080 Grade Increment Exam]

→ Draw the same diagram as in answer of Q. No. 6, but replace the word pure/impure silver plate by pure/impure gold plate and Silver nitrate solution by Auric Cyanide solution. [Verify this answer to your teacher]

10. Write difference between metal and non-metal on the basis of their density. [SLC 2068 E]

→ Metals have more density and non-metals have less density.

11. What are two main properties of metals that make it suitable for making pots and pans? [SLC 2058]

→ Metals are malleable and ductile.

→ Metals have metallic lusture.

12. You are given two objects, one of which gives sharp sound but doesn’t break into pieces when hammered, another object produces rough sound and break into pieces. Which one is metal? [SLC 2057]

→ The object which produces sharp sound and does not break when hammered is metal.

at No comments

Life Cycle of Honey bee - Class 10 science Guide [New Syllabus]

Posted on Wednesday, November 20, 2024

          UNIT - 3          

Honey Bee

Exercise

1. Choose the correct options for the questions below.

a. Which bee contains only 16 chromosomes?

i. Queen bee

ii. Worker bee

iii. Drone bee

iv. Queen and worker bee

b. From where is royal jelly produced?

i. from the gland at the head of queen bee

ii. from the gland at the head of drone

iii. from the gland at the head of worker bee

iv. from the salivary gland of worker

c. Which bee is formed when the larva is fed royal jelly continuously?

i. queen

ii. drone

iii. workers

iv. queen and worker bee

d. Which stage of the bee is shown in the given diagram?

i. egg

ii. larva

iii. pupa

iv. adult

e. Why is honey bee called a social insect?

i. It produces honey.

ii. It helps in pollination in plants.

iii. It lives in colony

iv. It is domesticated insect.

f. When the pollen baskets in the legs of worker bees are broken by certain means, which of the following functions cannot be performed by them?

i. collecting nectar

ii. constructing brood cell

iii. feeding royal jelly to larva

iv. collecting pollen from flower

g. Which of the following is the characteristic of the drone bee?

i. haploid, sterile, medium sized, hairy

ii. haploid, fertile, medium sized, hairy

iii. diploid, sterile, medium sized, smooth

iv. diploid, fertile, medium sized, hairy

h. Where does the queen bee store the sperms received from the drone bee after the nuptial flight?

i. pollen sac

ii. ovary

iii. sperm sac

iv. egg sac

2. Differentiate:

a. Drone and worker bee Drone Bee vs Worker Bee
Drone Bee Worker Bee
1. Male bee, whose primary role is reproduction. 1. Female bee, responsible for various tasks in the hive.
2. Larger than worker bees, with a broad body. 2. Smaller than drones, with a more slender body.
3. Does not have stinger and cannot defend the hive. 3. Has a stinger and can defend the hive if necessary.
4. Drones do not gather nectar or pollen. 4. Worker bees gather nectar, pollen, and water, and also make honey.
5. Drones die after mating with the queen. 5. Worker bees live longer and are responsible for the daily upkeep of the hive.

b. Queen bee and worker bee Queen Bee vs Worker Bee
Queen Bee Worker Bee
1. The queen bee is the reproductive female in the colony. 1. Worker bees are non-reproductive females responsible for tasks in the hive.
2. The queen is larger than the worker bees. 2. Worker bees are smaller than the queen bee and have a slender body.
3. The queen's main role is to lay eggs to ensure the colony's survival. 3. Worker bees gather nectar, pollen, and water, build honeycombs, and care for the brood.
4. The queen can live up to 5 years, but usually lives around 2-3 years. 4. Worker bees have a much shorter lifespan, usually living only a few weeks to a few months.
5. The queen has a fully developed reproductive system, producing pheromones to control the colony. 5. Worker bees do not lay eggs, and their reproductive system is underdeveloped.

c. Queen bee and drone Queen Bee vs Drone Bee
Queen Bee Drone Bee
1. The queen bee is the reproductive female of the hive. 1. Drone bees are the male bees whose primary role is to mate with the queen.
2. The queen bee is larger in size compared to drone bees. 2. Drone bees are larger than worker bees but smaller than the queen bee.
3. The queen bee lays all the eggs in the colony. 3. Drone bees do not lay eggs; their main role is reproduction.
4. The queen has a fully developed reproductive system and lives for several years. 4. Drone bees have underdeveloped reproductive organs and live only a few months.
5. The queen produces pheromones that control the behavior of the hive. 5. Drone bees do not produce pheromones and have no significant influence on the hive's behavior.

3. Give reason:

a. Honey bee is called a social insect.

→ Honey bee is called a social insect because they show highly social organization by dividing the colony into queen, workers, and drones based on their role in society, communicate through the waggle dance, cooperate in building and maintaining the hive, and work together for the survival of the colony.

b. Pasture land is required for bee farming.

→ Pasture land is required for bee farming because pasture land provides a diverse range of plants that bees searches widely for steady supply of nectar and pollen.

c. Drone dies after mating.

→ During mating, the part of the drone that enters the queen ruptures from his abdomen due to the force of the mating. Due to this reason drone bee dies after mating.

d. Bees are multipurpose insects.

→ Honey bees are considered multipurpose insects because they produce valuable products like honey, royal jelly and pollen as well as beeswax, and honey bee venom by selling which farmers can earn lot of money and promote economy of a nation.

4. Answer the following questions:

a. Write the various types of bees found in the hive.

→ Types of bees found in the hive are queen, drone and worker bees.

b. What is the function of the drone bee?

→ The function of drone bee is to mate with queen bee.

c. If the queen bee dies for some reason, who will control the hive?

→ If queen bee dies, the worker bees feed the larva royal jelly only so that new queen is formed. Hence, after death of queen bee, worker bees control the hive.

d. How does the queen bee control other members of the hive?

→ The queen bee controls other members of the hive by releasing chemical scents called pheromones.

e. Write the uses of honey.

→ Uses of honey are as follows:

- Honey is natural sweetener which has many medicinal properties.

- Enzymes contained in honey increases rate of digestion.

- It is used to cure cough and sore throat.

- It is also used in cosmetic products.

f. Describe the structure of the queen bee.

→ Structure of Queen bee:

- A queen bee is the largest bee in the colony.

- It is up to 2 cm in length.

- It has a stinger, functional ovaries and a spermathecal for collecting sperms during mating.

g. Mention the functions of the worker bee.

→ Functions of worker bee are as follows:

- They clean the hive and cling to honey comb to regulate temperature for egg, larva and pupa.

- Royal gland is developed in their head to produce royal jelly which is fed to larva and queen.

- They make honey comb and seal larval cell and honey cell using wax glands.

- They collect nectar, pollen, water etc.

h. Explain how the division of labor occurs in bees.

→ The division of labor in bees according to their types and age can be explained in table as follows: Bee Types Table
S.N. Type Age Function
1 Drone Throughout the life Fertilize queen bee and make hive warm.
2 Queen bee Throughout the life Lays eggs and regulates the activities of hive by secreting pheromones.
3 Worker 1-3 day Clean the hive and cling to the honey comb to provide warmth to egg larva and pupa.
4-6 days Feed honey bread to larvae.
7-11 days Royal gland is developed in their head to produce royal jelly which is fed to larva and queen.
12-17 days Four pair of wax glands are developed in their body, used for making honey comb and to seal larval cell and honey cell.
18-20 days Sting glands are developed to protect hive.
After 21 days Collect nectar, pollen, water, etc.

i. Explain the life cycle of honey bee with a diagram.

→ The life cycle of honey bee begins when the queen bee releases a pheromone that attracts drone bees. During the queen's nuptial flight, she mates with multiple drone bees, collecting sperm to fertilize eggs. A few days later, the queen starts laying eggs.

(i) Egg: The duration of egg for all bees is three days. From fertilized eggs develop queen and worker bees. Drone develops from unfertilized eggs.

(ii) Larva: After 3 days of laying eggs, eggs hatch into larvae. The larva is glutton. The larva may develop into queen bee or worker bee which depends upon the food fed to larva. All larvae feed on royal jelly for 3 days. After 3 days, the larva of future queen is continuously feed on royal jelly whereas the larva of future workers and drones feeds on beebread. It lasts for about 5.5 days for queen, 6 days for worker and 7 days for drones.

(iii) Pupa: The pupa does not feed or move but it’s structural changes continues. Three pairs of legs, wings and mouthpart are developed in this stage. It lasts for 8,12 and 14 days for queen, worker and drone respectively.

(iv) Adult: After many changes, pupa transforms to adult. The mandibles in mouth of newly formed adult bee chew the layer of wax sealed to the brood cell and emerge out. After they emerge, worker start to help others immediately. Generally, it takes 16, 21 and 24 days for queen, worker and drone respectively to reach adulthood from egg.

j. What is the process called in which a drone is developed from an unfertilized egg?

→The process in which a drone bee is developed from an unfertilized egg is called parthenogenesis.

k. When a farmer practices bee farming, then income of other farmers in that locality also increases. Justify your reason.

→ When a farmer practices bee farming, the bees goes outside to collect nectar and pollen thus helping in pollination process of plants and giving better yield to farmers. In this way, the income of other farmers in locality also increases.

l. Due to the problem of pasture land in the beekeeping area, beekeepers shifted the bees from there. After that, there was a reduction in the yield of mustard crops of nearby farmers. Based on this, explain the relationship between beekeeping and agricultural production.

→ The relationship between beekeeping and agricultural production can be explained as follows:

- Pollination: Bees play a crucial role in pollinating crops (including mustard) by transferring pollen from one flower to another which helps in the fertilization of plants leading to increased crop yield.

- Impact of Bee absence: When beekeepers moved their hives due to pasture land problems, the absence of bees resulted in reduced pollination due to which farmers experienced a decline in yield.

- Mutual Benefit: While bees rely on crops for nectar and pollen, farmers benefit from the improved yields due to enhanced pollination services provided by the bees.

In conclusion, beekeeping and agricultural production are closely linked as bees plays vital role in crop pollination.

m. Look at the concept map and complete it.

→

Bee Diagram
DRONE BEE
↑
Parthenogenesis
↑
bee
↓
Fertilization
↓
QUEEN
(Fertile)
WORKER
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Heredity (Part I) - Class 10 Science Guide [New Syllabus]

Posted on Monday, November 18, 2024

          Unit - 4           
Heredity (Part - I)

Exercise

1. Choose the correct option for the given questions.

a. How many pairs of sex chromosomes are found in the human cell?
i. 1 pair

ii. 22 pairs

iii. 23 pairs

iv. 46 pairs

b. What is a chromosome made up of?

i. DNA and RNA

ii. DNA and carbohydrate

iii. DNA and protein

iv. RNA and protein

C. What is the main function of sex chromosomes?

i. To determine physical characteristics

ii. To determine sex

iii. To increase immunity

iv. To determine the structure of the eye

d. What is the smallest unit of the chromosome that helps in the transmission of hereditary characteristics?

i. DNA

iii. Centromere

ii. Chromatid

iv. Gene

e. Which of the following statements is correct for mitotic cell division?

i. Four cells are formed at the time of cell division.

ii. Haploid cells are formed at the end of cell division. (Note that: Haploid cells are formed at the end of meiosis II)

iii. It has the main role to form gametes.

iv. This cell division helps to repair tissue.

f. A technician working in a radiotherapy laboratory was tested after a long time of marriage when there was no childbirth. After the test, it was found that his child production capacity was reduced because he worked in high-intensity radiation for a long time. Which part of the cell is affected in this case?

i. DNA

iii. Cytoplasm

ii. RNA

iv. Nucleus

g. If there is no DNA transcription in a cell. which process is affected?

i. Photosynthesis

ii. Sexual reproduction

iii. Protein synthesis

iv. Cell division

h. If a nucleotide is destructed during DNA replication, what happens to the organism?

i. Genetic disorder occurs

ii. It brings a problem in cell division

iii. It brings a problem in reproduction.

iv. The chromosome does not function.

i. Which of the following indicates the set of chromosomes in a cell of a woman?

i. 44+XY

ii. 44+XX

iii. 22+XY

iv. 22+XX

j. Which of the following statements is true?

i. Ovum contains only a Y chromosome and sperm contains an X chromosome.

ii. Ovum contains only an X chromosome and sperm contains a Y chromosome.

iii. Ovum contains only an X chromosome and sperm contains either an X or Y chromosome.

iv. Ovum and sperm both contain X and Y-chromosomes.

2. Write differences:

a. Autosome and sex chromosome Autosome vs Sex Chromosome
Autosome Sex Chromosome
1. Autosomes are non-sex chromosomes that determine most of an organism's traits. 1. Sex chromosomes determine the biological sex of an organism.
2. Humans have 22 pairs of autosomes. 2. Humans have 1 pair of sex chromosomes (XX for females, XY for males).
3. Autosomes are present in both males and females. 3. Sex chromosomes differ between males and females.
4. Autosomes carry genetic information related to traits such as eye color, height, etc. 4. Sex chromosomes carry genetic information related to gender determination and reproductive system development.
5. Example: Chromosome 1, Chromosome 2, etc. 5. Example: X chromosome, Y chromosome.

b. Mitosis and meiosis Mitosis vs Meiosis
Mitosis Meiosis
1. Mitosis is the process of cell division that results in two identical daughter cells. 1. Meiosis is the process of cell division that reduces the chromosome number by half, producing four genetically diverse gametes.
2. It occurs in somatic (body) cells. 2. It occurs in germ (sex) cells to produce sperm and eggs.
3. The chromosome number remains the same in the daughter cells (2n → 2n). 3. The chromosome number is halved in the daughter cells (2n → n).
4. Mitosis involves one division (prophase, metaphase, anaphase, telophase). 4. Meiosis involves two divisions (Meiosis I and Meiosis II), each with prophase, metaphase, anaphase, and telophase.
5. The result is two diploid (2n) daughter cells that are genetically identical. 5. The result is four haploid (n) daughter cells that are genetically different from each other and the parent cell.
6. Example: Cell division for growth, repair, and asexual reproduction. 6. Example: Cell division for sexual reproduction, forming gametes (sperm and eggs).

C. DNA and RNA DNA vs RNA
DNA RNA
1. DNA stands for Deoxyribonucleic Acid. 1. RNA stands for Ribonucleic Acid.
2. DNA is double-stranded in a double helix structure. 2. RNA is single-stranded.
3. DNA contains the sugar deoxyribose. 3. RNA contains the sugar ribose.
4. DNA has the base Thymine (T). 4. RNA has the base Uracil (U) instead of Thymine (T).
5. DNA is primarily located in the nucleus of the cell. 5. RNA is synthesized in the nucleus but is found in both the nucleus and the cytoplasm.
6. DNA stores genetic information and is responsible for heredity. 6. RNA plays a role in protein synthesis and gene expression.
7. DNA is more stable due to its double-stranded structure. 7. RNA is more prone to degradation due to its single-stranded nature.
8. Example: The human genome is made of DNA. 8. Example: mRNA, tRNA, and rRNA are types of RNA.

d. Haploid and Diploid Haploid vs Diploid
Haploid Diploid
1. Haploid cells have one set of chromosomes (n). 1. Diploid cells have two sets of chromosomes (2n).
2. Haploid cells are found in gametes (sperm and egg cells). 2. Diploid cells are found in somatic (body) cells.
3. Haploid cells are produced by meiosis. 3. Diploid cells are produced by mitosis.
4. Haploid cells have half the chromosome number of diploid cells. 4. Diploid cells have a full set of chromosomes, which are inherited from both parents.
5. Example: Human gametes (sperm and egg). 5. Example: Human somatic cells (skin cells, muscle cells, etc.).
6. Haploid number in humans is 23. 6. Diploid number in humans is 46 (23 pairs of chromosomes).
7. Haploid cells are not genetically identical; they have different combinations of chromosomes due to recombination. 7. Diploid cells are genetically identical to each other (except in the case of mutations).

3. Give reason:


a. Offspring have the same characteristics as their parents.

→ Offspring have the same characteristics as their parents because chromosomes in the nucleus replicate and divide during cell division, passing identical genetic information to daughter cells.

b. The male has a main role in the determination of sex.

→ The male has a main role in the determination of sex because he can contribute either an X or a Y chromosome, while the female only contributes an X chromosome. If the male contributes an X chromosome, the offspring will be female (XX), and if the male contributes a Y chromosome, the offspring will be male (XY).

C. Though males have both X and Y sex chromosomes, some of them have only male or only female kids.

→ The sperm cells of men hold approximately 50 percent of Y chromosome and other 50 percent of X chromosome. Therefore, despite having both X and Y chromosomes, there is possibility that some of them have kids of only one gender.

d. Meiotic cell division is also called reductional cell division.

→ Meiotic cell division is called reductional cell division because it reduces chromosome number half in the daughter cells if compared to their mother cell.

e. Mitotic cell division is also called equational cell division.

→ It’s because the daughter cells have same no. of chromosome as in mother cell.

f. Sexual reproduction is impossible without meiotic cell division.

→ Meiotic cell division maintains a definite and constant number of chromosomes in the sexual reproduction as it avoids the multiplication of chromosomes in offspring by reduction division. But in mitosis cell division no. of chromosomes is equal in daughter cell and reproduction is impossible. Thus, sexual reproduction is impossible without meiotic cell division.

g. Meiotic cell division brings variation.

→ During meiotic cell division, homologous chromosomes (one from each parent) align along their lengths. At specific points called chiasmata, the chromosomes cross over, breaking and rejoining to exchange genetic material. This recombination results in variation.

4. Answer the following question.

a. What is a gene?

→ The smallest fragment of DNA in a chromosome which codes or represents a specific character of an organism is called gene.

b. What is a chromosome? Clarify the role of chromosomes in the body of living beings.

→ The chromatin fibers inside nucleus of cell which becomes short, thickened and prominent during cell division are called chromosomes.

→ The role of chromosomes in the body of living beings are as follows:

- Somatic chromosomes determine the physical characteristics of an individual.

- Sex chromosomes determine the sex of an individual.

C. Explain the importance of mitotic cell division in the growth and development of the body.

→ Mitotic cell division plays a key role in physical growth, as the number of cells with same genetic makeup increases during cell division. It helps regenerate cells in injured area, returning them to original state. It maintains genetic stability.

d. Explain the role of mitosis and meiosis in the reproduction of organisms.

→ Mitosis and meiosis both play key roles in reproduction:

- Mitosis is responsible for the growth, repair, and asexual reproduction of cells. It produces two genetically identical daughter cells, maintaining the chromosome number of the original cell.

- Meiosis is involved in sexual reproduction, reducing the chromosome number by half to produce gametes. So, when fertilization occurs, the resulting offspring have the correct number of chromosomes. Meiosis also promotes genetic variation through recombination.

e. What will happen if meiotic cell division does not occur in the reproductive cell of an organism? Explain.

→ Without meiotic cell division, sexual reproduction would not be possible, and the organism would be unable to produce viable, genetically diverse offspring.

f. Clearly explain the role of genes in the transmission of hereditary characteristics in organisms.

→ The role of genes in transmission of hereditary characteristics in organisms are as follows:

· Genes are segments of DNA that carry the genetic information from parents to offspring.

· They determine inherited traits like eye color, height, and blood type based on the alleles inherited.

· Genes control the synthesis of proteins, which influence the physical and functional characteristics of an organism.

· Genetic variation arises through recombination during meiosis, leading to diversity in offspring.

g. How is sex determined in humans? Explain with a chart.

→ 
science class 10 guide book
Figure: Sex determination Chart


h. A woman is pregnant. What is her probability of giving birth to a daughter? Write in percent.

→ Her probability of giving birth to a daughter is 50%.

i. A couple gave birth to only a son. Does it mean that the testes of those male-produced sperms have Y-chromosomes only?

→ No, it doesn’t necessarily mean that. If a couple has a son, it means that the father’s sperm that fertilized the egg carried a Y chromosome, resulting in the combination XY, which is male. However, the father’s testes still produce both X and Y bearing sperm.

j. Complete the concept maps 'a' and 'b'. Write the differences between these processes.

Reproductive cell → cell division → Gamete [A]

Somatic Cell → cell division → Mitosis [B]

→ Differences between process A and B are as follows:

Process A:

-Reproductive cells divide by meiosis, producing four genetically different cells with half the chromosome number.

-Meiosis reduces the chromosome number by half (haploid) to ensure proper fertilization.

Process B:

-Somatic cells divide by mitosis, producing two identical cells.

-Mitosis maintains the same chromosome number in daughter cells (diploid).



Review of Chapter:


Ø The branch of biology that deals with the study of genes is called genetics.

Ø Cell division is the process by which a cell splits into two or more new cells, called daughter cells.

Ø There are 3 types of cell division- Amitosis, Mitosis and Meiosis cell division.

Ø Amitosis Cell division: it is simple and primitive type of cell division. The amitosis cell division is means of asexual reproduction which commonly occurs in some protozoa, bacteria, yeast etc.

Ø Mitosis cell division: mitosis is a type of cell division in which a single cell divides to form two daughter cells, having same no of chromosomes as in parent cell. It occurs in somatic and vegetative cells and hence called somatic cell division. This cell division completes in two phases (It actually completes in 3 phases but you don’t need to study the first phase called interphase where no visible changes occurs in nucleus): Karyokinesis and Cytokinesis. The significance of mitosis cell division are as follows:

- It maintains fixed no. of chromosomes in somatic cells.

- It helps in growth and development of new organs in multicellular organisms.

- It repairs old cells and regenerates the damaged tissues and organs.

- It helps in asexual reproduction.

Ø Meiosis Cell division: Meiosis is a type of cell division in which one mother cell produces four daughter cells; each daughter cell bears half the number of chromosome as compared to mother cell. This cell division completes in two phases namely Meiosis I and Meiosis II.

a. Meiosis I: The key processes involved in it are:

1. Crossing over occurs, leading to the exchange of genetic material between non sister chromatids, creating genetic variation.

2. Karyokinesis divides the nucleus into two haploid nuclei.

3. Cytokinesis forms two haploid cells.

Chromosome number is reduced to half, making it a reduction division.

b. Meiosis II: It is second phase. The key processes involved here are:

1. Each haploid cells undergoes a mitotic like division.

2. Karyokinesis divides nucleus again.

3. Cytokinesis forms a total of four haploid cells.

Chromosomes number remains unchanged in this phase, maintaining the haploid state.

Ø DNA:

Location: Found in prokaryotic cytoplasm, eukaryotic chromosomes, and virus capsids.

Structure: Made of two antiparallel strands; Basic unit is Nucleotide (nitrogen base + sugar + phosphate); Nitrogen bases are Adenine (A) which pairs with Thymine (T), and Guanine (G) which pairs with Cytosine (C)

Function: Carries hereditary information and codes traits through genes; also passes traits during cell division.

Significance: Variations in nucleotide sequences create diversity. Transcription of DNA forms RNA, aiding in protein synthesis.

Ø RNA:

Location: Found in the cytoplasm and nucleus of cells.

Structure: Single-stranded molecule; Basic unit is Nucleotide (nitrogen base + ribose sugar + phosphate); Nitrogen bases are Adenine (A) which pairs with Uracil (U), and Guanine (G) which pairs with Cytosine (C)

Function: Helps in protein synthesis by translating genetic instructions from DNA. Acts as a messenger (mRNA), transfer molecule (tRNA) or part of ribosomes (rRNA).

Significance: Essential for gene expression and protein formation. Temporary carrier of genetic information.

Ø CHROMOSOMES: The condensed form of chromatin fibres found within nucleus are called chromosomes. The no of chromosome for particular species is usually fixed but it varies considerably among species.

Human beings: 46 chromosomes

Gorillas: 48 chromosomes

Rat: 42 chromosomes

Ophioglossum: 1266 chromosomes

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