Life Cycle

Bee farming (apiculture) is beneficial for farmers because:

1. Extra income: Honey, beeswax, royal jelly, pollen and propolis can be sold, so farmers earn money with little land and low investment.
2. Better crop yield: Bees pollinate flowers while collecting nectar, which increases fruit and seed production of crops such as mustard, apple and buckwheat.

(It occurs in body/somatic cells for growth and repair, whereas meiosis occurs in reproductive cells to form gametes.)

A worker bee can be identified by:

1. It is small in size, and it is a sterile (undeveloped) female that does not lay eggs.
2. It has pollen baskets on the hind legs, a sting, and wax glands; it is the diploid ($2n = 32$) bee that does all the hive work.

Honey bee is called a social insect because:

1. It lives in a colony (hive) of thousands of bees, with a queen, drones and workers living together.
2. There is division of labour: the queen lays eggs, drones mate with the queen and workers do all other work. All depend on and help one another.

Mitosis is called equational cell division.

Reason: In mitosis the chromosomes are duplicated once and the cell divides once, so each daughter cell receives the same (equal) number and kind of chromosomes as the mother cell ($2n \to 2n$). The chromosome number is not changed.

• A is parthenogenesis: development of an unfertilized (haploid) egg into a drone bee.
• B is fertilization: an egg fused with sperm forms a diploid zygote that develops into a fertile queen bee (when fed royal jelly).

• P = Drone bee (male). It is formed from an unfertilized egg by parthenogenesis and is haploid ($n = 16$).
• Q = Worker bee (or queen bee). It is formed from a fertilized egg by fertilization and is diploid ($2n = 32$); a female with a sting.

• Y = Queen bee (fertile female). Her function is to lay eggs (up to about 1500-2000 a day) and to keep the colony together by her pheromone.
• Z = Worker bee (sterile female). Its functions are all the hive work: cleaning, feeding larvae, making wax and comb, guarding the hive and collecting nectar and pollen.

(X is the drone bee, formed by parthenogenesis.)

                      Honey bee (queen) lays eggs
                       /                        \
          Unfertilized egg                  Fertilized egg
                 |                                |
        PARTHENOGENESIS                     FERTILIZATION
                 |                                |
          Drone bee (n = 16)           Worker bee (2n = 32)
             (male)                     (sterile female)

• Drone bee develops by parthenogenesis (without fertilization).
• Worker bee develops by fertilization (a fertilized egg fed ordinary food).

1. Worker bees are sterile (undeveloped) females, small in size, and they are the most numerous in a hive (diploid, $2n = 32$).
2. They do all the work of the colony (cleaning, feeding larvae, making wax, guarding, collecting nectar and pollen) and have a sting, pollen baskets and wax glands. They live for only about 6 weeks.

(ii) 3. On the basis of work division there are three types of honey bees: the queen, the drones and the workers.

• 4-6 days: The worker feeds honey and bee-bread (pollen) to the older larvae.
• 18-20 days: The worker acts as a guard at the hive entrance, protecting the colony from enemies.

• 7-11 days: Worker bees produce royal jelly from their glands and feed it to the young larvae and the queen.
• 18-20 days: They work as guards at the entrance of the hive.

• 1-3 days: The worker cleans the hive (cells) and keeps it warm.
• 18-20 days: The worker guards the hive against enemies.

At 4-6 days the worker bee feeds honey and bee-bread (pollen) to the larvae.

After 21 days the worker bee goes outside the hive as a forager, collecting nectar, pollen and water.

(d) P-2, Q-4, R-1, S-3

• 1-3 days: cleaning of the hive (P-2).
• 4-6 days: feeding honey and honey bread (bee-bread) to the larvae (Q-4).
• 7-11 days: production of royal jelly (R-1).
• 12-17 days: development of wax glands and wax production (S-3).

(c) queen bee. A larva that turns into a pupa after about 5.5 days of feeding (on royal jelly) develops into a queen bee. Worker larvae pupate after about 6 days and drone larvae after about 6.5 days.

Yes, they can have their own baby even though they live far apart. This is possible by artificial insemination (AI).

How: The husband's healthy semen is collected, preserved (frozen) and sent to the wife's place. At the proper time of ovulation, a doctor injects the semen into the uterus/vagina of the wife with a syringe-like instrument. Fertilization then occurs inside her body, and the baby grows normally in her womb.

Differences between AI and IVF (IVF is used by couples with unhealthy reproductive health):

1. Improved breeds: Semen from a superior bull can fertilize many cows, so the offspring are healthy and give more milk and meat, increasing farm income.
2. Saves cost and prevents disease: Farmers need not keep a bull, and spread of sexually transmitted diseases is avoided. Semen can be stored and transported far away.

I would suggest keeping honey bees (apiculture).

1. Bees pollinate the flowers and crops they already grow, so the yield of fruits and seeds increases.
2. The villagers can sell honey, beeswax and royal jelly, which gives extra income with small investment and little land.

1. Drone is the male honey bee, formed from an unfertilized egg by parthenogenesis, so it is haploid ($n = 16$).
2. It is larger than the worker, has no sting, no wax glands and no pollen basket, does no hive work, and its only function is to mate with the queen. It dies after mating.

(i) The technology (IVF) is advantageous for infertile (childless) couples, e.g. when the woman's fallopian tubes are blocked, ovulation is poor or the husband's sperm count is low.

(ii) Flow chart of IVF

Ovarian stimulation with fertility medicines
                  |
                  v
Many eggs retrieved from the ovaries
                  |
                  v
Eggs fertilized with sperm in the laboratory
                  |
                  v
Embryos grow in the lab; the most viable are selected
                  |
                  v
Selected embryo transferred into the woman's uterus
                  |
                  v
Pregnancy and birth of the baby

(iii) No. It is not accessible to most Nepalese because it is very expensive, the treatment centres are few and mostly in big cities, trained specialists are limited, and many people lack awareness or have social misconceptions about it.

(b) Larva. The larva is the growing stage that eats continuously (honey, pollen and royal jelly fed by workers) and increases greatly in size, while egg, pupa do not feed.

1. The queen lays eggs (about 1500-2000 per day), thereby increasing the population of the colony.
2. She produces a pheromone (queen substance) that keeps the workers working and holds the colony together; she also mates with the drones.

Figure A is mitosis ($2n \to 2n$, two cells) and Figure B is meiosis ($2n \to n$, four cells).

(i) Figure B (meiosis) forms gametes.

(ii) Figure A (mitosis) forms daughter cells identical to the mother cell.

(iii) Importance of A (mitosis): it brings about growth, repair of damaged tissue and replacement of dead cells, and it is the basis of asexual reproduction.

(iv) Figure B (meiosis) keeps the chromosome number constant. It halves the number in gametes ($n$), and at fertilization two gametes unite to restore the $2n$ number of the parent.

This technology is artificial insemination (AI).

(i) Advantages

1. Semen of one superior male can be used for many females, so offspring of improved breed are obtained (more milk/meat).
2. There is no need to keep a male animal, which saves cost, and spread of sexual diseases is reduced.

(ii) Points to be considered

1. Insemination must be done at the proper time (heat/ovulation period) of the female.
2. The semen must come from a healthy, disease-free, good-breed male, be stored properly, and the work must be done by a trained person under hygienic conditions.

(i) A represents meiosis (reduction division), because it occurs in reproductive cells and leads to gamete formation. (Process P is meiosis; the $2n$ somatic division, Process Q, is mitosis.)

(ii) Difference: meiosis produces four daughter cells with half the chromosome number ($n$), whereas mitosis produces two daughter cells with the same chromosome number ($2n$) as the mother cell.

Advantages

1. Semen of a superior male can fertilize many females, so improved breed offspring are produced.
2. No need to keep a male animal, which saves cost, and sexual diseases are not spread.

Disadvantages

1. It needs trained technicians, equipment and proper storage of semen, which is costly and not available in remote areas.
2. If done at the wrong time or with unhygienic methods, it fails or causes infection; repeated use of the same male may reduce genetic variation.

Meiosis is called reduction division because the chromosome number is reduced to half (from $2n$ to $n$) in the daughter cells, which become gametes.

A diploid cell is a cell that contains two sets of chromosomes (one from each parent), written $2n$. Body (somatic) cells are diploid; in humans $2n = 46$.

In-vitro fertilization (IVF) is an assisted reproductive technology in which an egg and a sperm are fertilized outside the body, in a laboratory dish (in vitro).

Briefly: the woman is given medicines to produce several eggs; the eggs are collected and mixed with the husband's sperm. After fertilization the zygote/embryo is grown for a few days and then placed in the woman's uterus, where it develops into a baby. The baby born is called a test-tube baby. It helps couples who cannot conceive naturally.

The queen bee lays eggs (increasing the colony), whereas the drone bee only mates with the queen and does no other work.

In vitro fertilization (IVF) is responsible. The egg and sperm of the couple are fertilized in the laboratory and the embryo is placed in the uterus of a surrogate mother, who carries it to birth.

Boon: Couples in which the wife cannot carry a pregnancy (e.g. a damaged or absent uterus) can still have their own genetic child, which brings happiness to the family.

(d) In a hive the queen bee lives the longest. The queen lives for 2-5 years, while workers live only about 6 weeks and drones a few months. Feeding larvae and warming the hive are worker jobs, and a hive has only one queen.

IVF is a boon because it enables couples who cannot conceive naturally (blocked tubes, low sperm count, etc.) to have their own biological baby.

The organization should adopt artificial insemination (AI).

Advantage: Semen from one superior bull can be used to fertilize many cows at a time, giving improved-breed offspring with high milk yield, and there is no need to keep many bulls.

Marchantia reproduces asexually by gemmae (and fragmentation). Characteristics:

1. Division is by mitosis, so the new plants are genetically identical to the parent.
2. Small bud-like gemmae form in cup-shaped gemma cups on the thallus; they are splashed out by rain and grow into new plants. Also, broken parts of the thallus can grow into new plants.

(a) Meiosis (reduction division) takes place during the formation of gametes; it halves the chromosome number.

(b) Mitosis takes place after the formation of the zygote; it makes the cells of the embryo for growth and development.

The figure shows in vitro fertilization (IVF), the test-tube baby technique. Two advantages:

1. It enables childless couples (blocked fallopian tubes, low sperm count, poor ovulation) to have their own baby.
2. A woman who cannot carry a pregnancy can use a surrogate mother, and healthy embryos can be selected and checked for disease before transfer.

Artificial insemination (AI) is the technique in which semen is collected from a male animal and placed by an instrument into the uterus/reproductive tract of the female at the time of heat, without natural mating.

Reason farmers prefer it: Semen of a superior breed bull can be used for many cows, so the calves are of improved breed (more milk) and the farmer saves the cost of keeping a bull.

The major function of a drone bee is to mate with the queen bee (during the nuptial flight) and fertilise her eggs.

Living beings reproduce to produce new individuals of their own kind, so that their species continues from generation to generation and does not become extinct.

Pollination is the transfer of pollen grains from the anther of a flower to the stigma of the same or another flower.

Spirogyra reproduces by fragmentation. Its filament breaks into pieces, and each piece grows into a new filament.

Binary fission is the common asexual reproduction in amoeba: the nucleus divides first and then the cytoplasm, forming two daughter amoebae.

Since the branches of the lemon plant are high above the ground, they cannot be bent down into the soil, so air layering (gootee or marcotting) can be applied.

Process:

1. Select a healthy branch and remove a ring of bark about 2-3 cm wide.
2. Cover the bared part with moist soil, moss or coconut fibre and wrap it with polythene, tying both ends firmly.
3. Keep it moist. After a few weeks roots grow from the covered part.
4. Cut the branch just below the rooted part and plant it in soil as a new plant.

Diagram:

   Parent lemon plant
        |
        |-- branch
            |  [ring of bark removed]
            |  [moist soil/moss wrapped in polythene]  <- roots form here
            |  cut below the roots to separate

1. New plants are exactly like the parent plant (same flower colour, size and quality), so good varieties of ornamental plants such as rose are preserved.
2. New plants grow and flower earlier than those grown from seeds, and many plants can be produced quickly and cheaply from one plant (by cutting, layering or grafting).

Honey bee shows complete metamorphosis, with four stages: egg, larva, pupa and adult.

Egg --> Larva --> Pupa --> Adult
(laid in a    (fed by       (sealed in    (queen, worker
 hive cell)    workers)      the cell)     or drone)

• Egg: the queen lays a fertilised egg (32 chromosomes) or an unfertilised egg (16 chromosomes) in a cell of the comb.
• Larva: it hatches and is fed by worker bees. A larva fed royal jelly throughout becomes a queen; otherwise it becomes a worker.
• Pupa: the larva stops feeding, the cell is sealed with wax, and the body organs are formed.
• Adult: the adult bee comes out of the cell.

OR: differences between worker bee and queen bee

Rhizopus: by spores. The hypha bears a sporangium full of spores. When the sporangium bursts, the spores are released and each grows into a new Rhizopus on suitable moist food.

 Sporangium (full of spores)
      |
  sporangiophore (erect hypha)
 ----------------------------
  rhizoids (in the substrate)      -> spores released -> new Rhizopus

Hydra: by budding. A small outgrowth (bud) appears on the parent's body, grows tentacles and a mouth, and finally separates to live as a new hydra.

 Parent hydra  --  bud (small outgrowth)  -->  bud grows  -->  separates as young hydra

(a) Process A is gametogenesis (formation of gametes).

(b) Process B is fertilisation, and it is of two types: external fertilisation and internal fertilisation.

Technique: tissue culture, which can produce many identical plants in a short time from a tiny part of a single plant.

Process:

1. A small piece of tissue (e.g. a shoot tip) is cut from a healthy rose plant.
2. It is sterilised and placed on a sterile nutrient medium containing sugar and growth hormones in a test tube or flask.
3. The tissue divides into an undifferentiated mass of cells (callus).
4. The callus is shifted to another medium, where it forms shoots and roots.
5. The small plantlets are hardened and transplanted to soil, giving the 20 or more rose plants.

Why it is advantageous for agriculture, forestry and horticulture: it gives a large number of uniform, high-quality, disease-free plants of the desired variety within a short time and in a small space.

Two other reasons:

1. Rare and endangered plants can be multiplied and conserved.
2. Plants can be produced throughout the year, independent of season.

(a) Part A (the ovary) is formed at the base of the pistil (carpel), the female part of the flower.

(b) The ovule inside the ovary forms the seed.

(c) The fusion of the egg cell (C) and the male gamete forms a zygote.

Eggs A and B have 32 chromosomes, so they are fertilised eggs and give females. A, fed ordinary food, becomes a worker; B, fed royal jelly, becomes a queen. Egg C has 16 chromosomes, so it is unfertilised and becomes a drone.

(a) Egg C forms the drone bee.

(b) The bee from egg B (the queen) can lay eggs.

(c) The bee from egg A (the worker) forms royal jelly, using glands in its head.

(d) The bee from egg B (the queen) goes on the nuptial (mating) flight, followed by the drones, to mate.

• A = Drone bee (male), formed from an unfertilized egg by parthenogenesis.
• B = Queen bee, formed from a fertilized egg; the fertile female that lays eggs.

• X = Fertile queen bee, formed by fertilization: diploid, $2n = 32$ chromosomes.
• Y = Drone bee, formed by parthenogenesis from an unfertilized egg: haploid, $n = 16$ chromosomes.

(Sterile worker bees are also diploid, 32.)

IVF (in vitro fertilization) helps a woman to become a mother when:

1. Her fallopian tubes are blocked or damaged, so the egg and sperm cannot meet.
2. The husband's sperm count is low or the sperms are weak, or the woman has problems in ovulation, so natural fertilization fails.

(a) AI has brought happiness to farmers

1. Semen of a high-quality bull can be used for many cows, so the offspring give more milk and meat, which raises the farmer's income.
2. The farmer need not keep or feed a bull, which saves cost, and it prevents spread of sexual diseases and gives animals of desired breed.

(b) IVF is a boon for childless couples

1. It lets couples with blocked tubes, low sperm count or ovulation problems, who cannot conceive naturally, have their own biological child.
2. If the woman cannot carry a pregnancy, the embryo can be placed in a surrogate mother, so the couple still gets a child of their own, bringing happiness to the family.