Lesson 3: Life Processes in Living Organisms Part-2

Rule 1: Fission and budding — Asexual reproduction happens by mitosis. In binary fission (द्विभाजन) one cell divides into two: simple in Amoeba, transverse (across) in Paramecium and longitudinal (lengthwise) in Euglena. In multiple fission (बहुविभाजन) the cell inside a cyst divides into many (Amoeba). In budding (मुकुलन) a small bud grows on the parent and then separates (yeast).

In the figure : In the figure fission and budding.

• Easy : Easy: one Amoeba divides by binary fission into 2; after 4 divisions there are 2⁴ = 16 Amoebae.
• Medium : Medium: Paramecium splits across its body, Euglena splits along its length; the direction is the difference.
• Exam-type : Exam: yeast does not split in half; a small bud forms and later separates, which is called budding.

Spot the difference

Rule 1: Asexual methods in many-celled organisms — Fragmentation (खंडीभवन): the body breaks into pieces that each grow into a new organism (Spirogyra, Sycon). Regeneration (पुनरुद्भवन): a lost part or a piece grows into a whole animal (Planaria). Budding: a bud on the parent grows into a new individual (Hydra). Vegetative propagation: potato eyes, leaf buds of Bryophyllum, nodes of sugarcane. Spore formation (बीजाणू निर्मिती): tiny spores in a sporangium (Mucor).

In the figure : In the figure the asexual methods in many-celled organisms.

• Easy : Easy: a piece of a Planaria cut into 3 parts can grow into 3 new worms by regeneration.
• Medium : Medium: a farmer plants sugarcane pieces with nodes; each node can give a new plant. This is vegetative propagation.
• Exam-type : Exam: identify the method – Hydra with a bud (budding); Mucor spores (spore formation); Spirogyra breaks (fragmentation).

Spot the difference

Rule 1: The flower — Sexual reproduction needs two gametes formed by meiosis; fertilization gives a diploid zygote. A flower has the calyx (निदलपुंज) and corolla (दलपुंज) as accessory parts, and the androecium (पुमंग, male) and gynoecium (जायांग, female) as essential parts. A bisexual flower has both (Hibiscus); a unisexual flower has only one (Papaya).

In the figure : In the figure the parts of a flower.

• Easy : Easy: a Hibiscus flower has both stamens and pistil, so it is bisexual.
• Medium : Medium: papaya male flowers have only stamens, female flowers only a pistil; they are unisexual.
• Exam-type : Exam: essential parts are the androecium and gynoecium because they make gametes; calyx and corolla are only accessory.

Rule 2: Pollination and double fertilization — After pollination, the pollen grain forms a pollen tube that carries two male gametes to the ovule. Double fertilization (द्विफलन): one male gamete joins the egg to form the zygote, and the other joins the polar nuclei to form the endosperm (food store). The ovule becomes the seed and the ovary becomes the fruit.

In the figure : In the figure double fertilization in a flower.

• Easy : Easy: the zygote grows into the embryo, the baby plant inside the seed.
• Medium : Medium: why is it called double fertilization? Two male gametes take part – one with the egg, one with the polar nuclei.
• Exam-type : Exam: arrange – pollination → pollen tube → double fertilization → zygote and endosperm → seed and fruit.

Spot the difference

Rule 1: Human reproductive systems — In males, the testes (वृषण) lie in the scrotum and make sperms by meiosis. In females, there are ovaries (अंडाशये), oviducts (अंडवाहिन्या), the uterus (गर्भाशय) and the vagina.

• Easy : Easy: the sperm is made in the testes and the egg in the ovary.
• Medium : Medium: sperms and eggs are both gametes, made by meiosis, so each has 23 chromosomes.
• Exam-type : Exam: name the organ where the embryo gets implanted – the uterus.

Rule 2: Fertilization to birth — Fertilization is internal and happens in the oviduct. The zygote divides to form an embryo, which is implanted in the uterus. The placenta (वार) nourishes the embryo, and development takes about nine months. The sex of the child is decided by the father's sperm, which carries either X or Y: X with the mother's X gives a girl (XX), Y gives a boy (XY).

In the figure : In the figure the steps from fertilization to birth.

• Easy : Easy: the placenta supplies the embryo with oxygen and food.
• Medium : Medium: a sperm with Y chromosome fertilizing an egg gives XY, a boy; the egg always carries X.
• Exam-type : Exam: it is the father's sperm that decides the sex of the baby, because the mother can give only X.

Spot the difference

Rule 1: The menstrual cycle — The cycle lasts 28–30 days and is controlled by the hormones FSH, LH, estrogen and progesterone. Ovulation (अंडोत्सर्ग) is the release of an egg from the ovary. If the egg is not fertilized, menstruation (मासिक पाळी) occurs and lasts about five days.

In the figure : In the figure the menstrual cycle.

• Easy : Easy: if a cycle is 28 days and menstruation starts on day 1, the next starts on day 29.
• Medium : Medium: if menstruation lasts 5 days in a 28-day cycle, the remaining 28 − 5 = 23 days are other phases.
• Exam-type : Exam: menstruation occurs because the egg was not fertilized and the thickened uterine lining is shed.

Rule 2: Reproductive technology and health — IVF (in vitro fertilization): the egg and sperm are joined outside the body and the embryo is placed in the uterus. In surrogacy (सरोगसी) another woman carries the baby. A sperm bank stores sperms. Twins can be monozygotic (identical, from one zygote) or dizygotic (from two zygotes). Hygiene is important in reproductive health.

• Easy : Easy: a baby born by IVF is a normal baby; only the meeting of egg and sperm happened outside the body.
• Medium : Medium: identical twins come from one zygote and have the same sex; dizygotic twins come from two eggs and may differ.
• Exam-type : Exam: monozygotic means from one zygote; dizygotic means from two zygotes.

Spot the difference