Where Mindful Learning Begins
Where Mindful Learning Begins
Class 10 Science NCERT Solutions Chapter 7 (CBSE 2026-27) — every in-text question, every embedded Activity question, and all 11 back-of-chapter Exercises on this one page, solved with the reasoning behind each answer.
How do Organisms Reproduce? opens by asking why organisms reproduce at all, before showing that reproduction, at its core, is about copying DNA — and that the small, unavoidable errors in this copying are the very source of the variation that helps species survive. It then works through asexual reproduction (fission, fragmentation, regeneration, budding, vegetative propagation, spore formation), sexual reproduction in flowering plants (pollination, fertilisation, seed and fruit formation), and finally human reproduction — puberty, the male and female reproductive systems, pregnancy, menstruation, and reproductive health, including contraception. These NCERT solutions work through every Activity-based question — the yeast and mould comparison, the potato and money-plant cuttings, the flower dissection — and the full 11-question Exercise set in detail, making this one of the most concept-dense chapters in the biology portion of the Class 10 Science syllabus.
How do Organisms Reproduce? starts from an unusual angle for a biology chapter — not "how" but "why". Reproduction isn't needed to keep an individual organism alive, so the chapter builds its explanation from DNA copying upward: copying DNA lets an organism pass its body-design blueprint to offspring, small copying errors create variation, and that variation is what lets populations survive when their environment changes. From there it surveys the many ways organisms actually reproduce — the simple, single-parent methods of asexual reproduction (fission, fragmentation, regeneration, budding, vegetative propagation, spore formation), why sexual reproduction generates variation faster by combining DNA from two individuals, how flowering plants achieve this through pollination and fertilisation, and finally how the same process plays out in humans, from puberty through the male and female reproductive systems to pregnancy, menstruation, and reproductive health. Every question woven through the chapter is solved here, section by section, in the order the textbook presents it: the three "QUESTIONS" boxes after Sections 7.1 through 7.3, the questions embedded directly inside Activities, and the full 11-question Exercise set at the end.
Why DNA copying matters, how variation helps species survive, and the many single-parent modes — fission, budding, regeneration, vegetative propagation, spores.
Flower structure, pollination vs fertilisation, and how a zygote develops into a seed inside a ripening fruit.
Puberty, the male and female reproductive systems, fertilisation and pregnancy, menstruation, and reproductive health including contraception.
DNA carries the blueprint/information for an organism's body design (through the proteins it codes for). Accurate copying of DNA ensures new individuals resemble their parents and belong to the same species. At the same time, since DNA copying is never perfectly accurate, small variations get introduced each generation — this variation is the basis for evolution and helps ensure the long-term survival of species when environmental conditions change.
A variation may or may not help an individual organism — some variations could even be harmful, or make the individual less suited to survive. But at the level of a population/species, having a range of variations increases the chance that at least some individuals will survive if the environment changes drastically. This way, variation increases the likelihood of the species' survival, even if it doesn't benefit (or even harms) any single individual.
In binary fission, one parent cell divides to form two daughter cells (e.g., bacteria, Amoeba). In multiple fission, one parent cell divides simultaneously into many daughter cells at once (e.g., Plasmodium, the malarial parasite).
Spores are covered by thick, protective walls that let them survive harsh or unfavourable conditions (like dryness) for long periods. When conditions become favourable again (e.g., contact with a moist surface), spores can germinate into new individuals. This helps organisms like bread mould reproduce in large numbers and increases their chances of survival and spreading to new locations.
In complex, highly organised multi-cellular organisms, cells are specialised into tissues, tissues into organs, and organs are arranged in very specific positions to perform coordinated functions. If such an organism were cut into pieces, it's highly unlikely each piece would contain the full range of specialised cell types (including regenerative cells), in the right arrangement, to grow back a complete individual. This level of complexity makes piece-by-piece regeneration impractical for advanced organisms, unlike simple organisms such as Hydra or Planaria.
DNA copying is essential because DNA carries the genetic information/blueprint for an organism's body design. For a new individual to be created that resembles its parent and belongs to the same species, an accurate copy of this genetic information must be passed on. Without DNA copying, no new individual could form with the appropriate cellular apparatus to carry out life processes and develop the correct body design.
Pollination is the transfer of pollen grains from the anther (stamen) to the stigma of a flower — the same flower (self-pollination) or a different flower (cross-pollination). Fertilisation is the fusion of the male germ-cell (from the pollen, after it grows a tube through the style) with the female egg cell in the ovule, forming a zygote. Pollination is the physical transfer of pollen and happens before fertilisation, the actual fusion of germ cells.
The seminal vesicles and the prostate gland add their secretions to the sperms as they travel through the vas deferens. These secretions form a fluid that makes sperm transport easier and also provides nutrition to the sperms.
Common changes (also in boys): growth of thick hair in new areas (armpits, genital area, which may also darken), thinner hair on arms/legs/face, oilier skin, and pimples.
Changes specific to girls: increase in breast size, darkening of the skin of the nipples, and the start of menstruation.
The embryo gets nourishment from the mother's blood through a special tissue called the placenta — a disc embedded in the uterine wall, with villi on the embryo's side surrounded by blood spaces on the mother's side. This provides a large surface area for glucose and oxygen to pass from mother to embryo (and for embryonic waste to pass into the mother's blood for removal).
No. A copper-T is placed inside the uterus to prevent pregnancy — it does not act as a physical barrier against infection transmission during intercourse. Protection against sexually transmitted diseases requires a barrier method such as a condom.
In Activity 7.1, yeast (unicellular) reproduces by budding — small buds grow out from the parent cell, enlarge, and eventually separate into new independent cells; under the microscope you can see chains/clusters of budding cells. In Activity 7.2, bread mould (Rhizopus, a simple multicellular fungus) grows as thread-like hyphae over the bread's surface, and after a few days develops tiny sporangia that produce spores — reproducing via spore formation rather than budding. Both are asexual, but yeast buds (a unicellular process) while mould forms spores (from a simple multicellular structure).
A normal (non-dividing) Amoeba slide shows a single, irregularly shaped cell with pseudopodia used for movement and feeding. The binary fission slide shows the nucleus and cytoplasm dividing into two, with the cell elongating and gradually pinching apart into two separate daughter Amoebae. Since fission in Amoeba can occur in any plane, this shows a different pattern from organisms like Leishmania, where fission occurs in a fixed orientation relative to certain structures.
Spirogyra breaks into fragments upon maturation because it has a very simple body organisation — a filamentous, multicellular organism whose cells are not organised into distinct specialised tissues. Since there's no complex tissue/organ structure to disrupt, the filament can break at any weak point, and each fragment, containing complete cells, can grow into a new individual by further cell division. Because Spirogyra's cells are essentially uniform along the filament (not differentiated into distinct tissues), no different tissues can be identified under the microscope.
Petals are usually brightly coloured and help attract insects and other pollinators to the flower, aiding pollination. Sepals are usually green, leaf-like structures that protect the flower bud before it blooms.
The remains of the style and stigma can sometimes still be seen persisting at the tip of a mature fruit (e.g., a small dried structure at the tip of a tomato or apple).
Advantages of seed formation: seeds allow offspring to be dispersed to new locations (via wind, water, or animals), protect the embryo (with a tough seed coat) during unfavourable conditions until it's suitable to germinate, and provide the embryo with stored food to support its initial growth after germination.
Only the potato pieces that contain a notch or bud (the "eyes" of the potato) give rise to fresh green shoots and roots. Pieces without a notch/bud don't develop into new plants, since the bud is the site from which new growth originates.
The pieces containing at least one leaf (with a node) grow and give rise to fresh new leaves and roots when placed in water, while pieces cut from between two leaves (with no node) do not grow. This shows that new growth in money-plant cuttings originates specifically from nodes — the points where leaves attach to the stem — demonstrating vegetative propagation from stem cuttings.
As the text discusses, poor living standards are more closely linked to inequality in the distribution of resources in society than to population size alone — while an expanding population does make it harder to improve everyone's standard of living, if resources were shared more equitably, population size alone would be a far less significant factor.
Answer: (b) Yeast
Answer: (c) Vas deferens — this is part of the male reproductive system.
Answer: (d) pollen grains
Sexual reproduction combines DNA (genetic variations) from two different individuals, creating new and more varied combinations of variation at a faster rate than asexual reproduction (which relies only on the slow accumulation of copying errors within a single lineage). This greater variation is advantageous because it increases the chances that some individuals will survive and adapt if environmental conditions change drastically, improving the long-term survival and stability of the species.
The testes perform two main functions: (i) they produce sperms (male germ-cells), and (ii) they secrete the hormone testosterone, which regulates sperm formation and also brings about the physical changes seen in boys at puberty.
Every month, the uterus prepares to receive and nourish a fertilised egg by thickening its lining and increasing its blood supply. If the released egg is not fertilised, this thickened lining is no longer needed, so it breaks down and is shed from the body through the vagina, along with some blood and mucus. This monthly shedding of the uterine lining is called menstruation.
A longitudinal section of a flower shows, from outside to inside: sepals (outermost, protective, usually green), petals (often brightly coloured, attract pollinators), stamens (male part — a filament topped by an anther, which produces pollen grains), and the pistil at the centre (female part — a sticky stigma at the top, a style in the middle, and the swollen ovary at the base, containing ovules).
Unicellular organisms reproduce through simple methods like fission (binary or multiple) or budding, where the entire single cell divides or buds off to directly form new individuals. Multicellular organisms, because of their more complex body organisation (specialised tissues and organs in specific positions), cannot simply divide cell-by-cell; instead they use more complex modes — regeneration, budding (in simple organisms like Hydra), vegetative propagation (in plants), spore formation (in simple organisms like bread mould), or sexual reproduction using dedicated reproductive cells/organs.
Reproduction lets organisms maintain their body-design features (through relatively consistent DNA copying), so a population keeps fitting into and successfully using its ecological niche generation after generation. At the same time, the small variations generated during DNA copying provide a range of individuals within the population, some of whom may be better suited to survive if the niche changes (e.g., due to temperature changes or resource availability). This combination — a successful body design, plus room for variation — helps populations of a species remain stable and persist over time, even as environmental conditions change.
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