In a bisexual flower, in spite of the young stamens being removed artificially, the flower produces fruit. Provide a suitable explanation for this situation.
The pistil remains intact and cross pollination occurs, leading to fertilisation and formation of fruit.
Can you consider cell division as a type of reproduction in unicellular organisms? Give one reason.
Yes, because cell division forms two daughter cells, resulting in the production of more individuals of the organism.
What is a clone? Why do offsprings formed by asexual reproduction exhibit remarkable similarity?
A clone is an offspring of an organism formed by asexual reproduction. They exhibit remarkable similarity because they possess exact copies of the DNA of their parent.
Explain how offsprings and parents of organisms reproducing sexually have the same number of chromosomes.
Reduction division (meiosis) during gamete formation halves the chromosome number in both male and female gametes. When these gametes fuse during fertilisation, the original number of chromosomes is restored in the offspring.
Colonies of yeast fail to multiply in water, but multiply in sugar solution. Give one reason for this.
Sugar provides energy for sustaining all life activities in yeasts. In water, they fail to reproduce due to inadequate energy in their cells.
Why does bread mould grow profusely on a moist slice of bread rather than on a dry slice?
Moisture is essential for the growth of hyphae. A moist bread slice offers moisture and nutrients, enabling the mould to grow profusely. A dry slice offers nutrients but lacks moisture, preventing hyphal growth.
Give two reasons for the appearance of variations among the progeny formed by sexual reproduction.
Sexual reproduction involves two parents with different sets of characters.
The gene combinations are different in gametes.
Would a Planaria cut vertically into two halves regenerate into two individuals? Complete the diagram by indicating the regenerated regions.
Yes. The shaded regions in Figures D and E represent the regenerated halves.
Gather information about chromosome numbers of some animals and plants. Correlate the number with the size of organism and answer the questions.
(a) Do larger organisms have more chromosomes?
(b) Can organisms with fewer chromosomes reproduce more easily?
(c) Justify: More chromosomes mean greater DNA content.
(a) There is no relationship between size of organism and its chromosome number.
(b) No. Reproduction follows a common pattern and is not dependent on chromosome number.
(c) Since chromosomes contain DNA, more chromosomes indicate more DNA quantity.
In tobacco plant, the male gametes have twenty-four chromosomes. What is the number of chromosomes in the female gamete and in the zygote?
The female gamete has 24 chromosomes and the zygote has 48 chromosomes.
Why cannot fertilisation take place in flowers if pollination does not occur?
Fertilisation requires both male and female gametes. If pollination does not occur, the male gamete is not available, hence fertilisation cannot take place.
Is the chromosome number of zygote, embryonal cells, and adult of an organism always constant? How is this constancy maintained?
Yes. The constancy is maintained because cells in all these stages undergo mitotic divisions, preserving chromosome number.
Where is the zygote located in the flower after fertilisation?
The zygote is located inside the ovule present in the ovary.
Reproduction is linked to stability of population of a species. Justify.
DNA is copied from one generation to the next with high consistency and minor variations, leading to stability of species.
How are general growth and sexual maturation different from each other?
General growth refers to overall physical development such as increase in height and weight. Sexual maturation is specific to puberty-related changes such as cracking of voice, new hair patterns, and development of breasts in females.
Trace the path of sperm during ejaculation and mention the glands involved and their functions.
Sperms travel from testes into the vas deferens and then enter the urethra before ejaculation. Secretions of seminal vesicles and prostate gland provide nutrition and aid sperm transport.
What changes are observed in the uterus if fertilisation does not occur?
The thick and spongy lining of the uterus breaks and comes out through the vagina as blood and mucus.
What changes are observed in the uterus subsequent to implantation of the young embryo?
The uterine wall thickens and becomes richly supplied with blood. Placenta develops to provide nutrients and oxygen to the embryo.
What are the benefits of using mechanical barriers during sexual act?
Mechanical barriers like condoms prevent sperms from reaching the egg, avoiding pregnancy. They also prevent transmission of infections.
In the given diagram, label the parts and mention their functions.
(a) Ovary – Production of egg
(b) Oviduct – Site of fertilisation
(c) Uterus – Site of implantation
(d) Vagina – Entry of sperms
What is the ratio of chromosome number between an egg and its zygote? How is a sperm genetically different from an egg?
The ratio is 1:2. Sperms contain either an X or Y chromosome, whereas an egg always has an X chromosome.