Q1. What is double fertilization? Why is it called so? 2M

Answer: Double fertilization is the process unique to angiosperms where two male gametes participate in two separate fusion events:
1. Syngamy: One male gamete fuses with egg cell to form diploid (2n) zygote
2. Triple fusion: Another male gamete fuses with two polar nuclei to form triploid (3n) endosperm
It is called "double" because fertilization occurs twice in the same embryo sac.

Q2. Differentiate between autogamy and geitonogamy. 2M

Answer:
Autogamy: Transfer of pollen grains from anther to stigma of the same flower. True self-pollination.
Geitonogamy: Transfer of pollen grains from anther of one flower to stigma of another flower on the same plant. Functionally cross-pollination but genetically self-pollination.

Q3. What is the significance of pollination? 2M

Answer: Pollination is essential for:
1. Transfer of pollen grains from anther to stigma
2. Enables fertilization to occur
3. Leads to seed and fruit formation
4. Cross-pollination brings genetic variation
5. Essential for crop production and plant reproduction

Q4. Distinguish between spermatogenesis and oogenesis. 3M

Answer:

Q5. What is menstrual cycle? Name the hormones that regulate it. 3M

Answer: The menstrual cycle is a cyclic event occurring in sexually mature human females approximately every 28 days. It prepares the uterus for pregnancy.

Regulating hormones:
1. FSH (Follicle Stimulating Hormone): Stimulates follicle development
2. LH (Luteinizing Hormone): Triggers ovulation
3. Estrogen: Proliferation of endometrium
4. Progesterone: Maintains endometrium for implantation

Q6. What is the role of placenta during pregnancy? 3M

Answer: Placenta is a special tissue connecting fetus to mother through umbilical cord. Its roles:
1. Nutritive: Provides nutrients and oxygen from mother to fetus
2. Excretory: Removes waste products from fetal blood
3. Respiratory: Acts as lungs for fetus (O₂ and CO₂ exchange)
4. Endocrine: Secretes hCG, hPL, estrogen, progesterone
5. Barrier: Protects fetus from harmful substances (to some extent)

Q7. Name any four methods of contraception and their mode of action. 2M

Answer:
1. Condoms: Barrier method preventing sperm from meeting ovum
2. IUDs (CuT): Copper ions suppress sperm motility
3. Oral Pills: Hormones prevent ovulation by inhibiting FSH and LH
4. Vasectomy: Surgical method blocking vas deferens to prevent sperm transport

Q8. What are STIs? Name any two bacterial and two viral STIs. 2M

Answer: STIs (Sexually Transmitted Infections) are diseases transmitted through sexual contact.

Bacterial STIs:
1. Gonorrhea (caused by Neisseria gonorrhoeae)
2. Syphilis (caused by Treponema pallidum)

Viral STIs:
1. Genital Herpes (Herpes simplex virus)
2. AIDS (Human Immunodeficiency Virus - HIV)

Q1. Describe the process of double fertilization in flowering plants. 5M

Answer:
Double fertilization is unique to angiosperms and involves two fusion events:

Process:
1. Pollen Germination: Compatible pollen grain germinates on stigma forming pollen tube
2. Pollen Tube Growth: Tube grows through style guided by chemotropic signals, enters ovule through micropyle
3. Entry into Embryo Sac: Pollen tube enters embryo sac, releases two male gametes
4. First Fusion - Syngamy: One male gamete (n) fuses with egg cell (n) forming diploid zygote (2n). This develops into embryo.
5. Second Fusion - Triple Fusion: Another male gamete (n) fuses with two polar nuclei (n+n) forming triploid primary endosperm nucleus (3n). This develops into endosperm.

Significance:
- Ensures genetic diversity
- Endosperm provides nutrition to developing embryo
- Economical use of male gametes
- Confirms seed viability

Q2. Describe the structure and functions of human male reproductive system. 5M

Answer:
The male reproductive system consists of:

1. Testes (Primary Sex Organs):
- Paired oval structures located in scrotum
- Contain seminiferous tubules where spermatogenesis occurs
- Leydig cells produce testosterone hormone

2. Accessory Ducts:
- Rete testis: Network of tubules collecting sperms from seminiferous tubules
- Vasa efferentia: Transport sperms from rete testis to epididymis
- Epididymis: Stores and matures sperms
- Vas deferens: Muscular tube transporting mature sperms
- Urethra: Common passage for urine and semen

3. Accessory Glands:
- Seminal vesicles: Secrete fructose (energy for sperms), prostaglandins
- Prostate gland: Secretes alkaline fluid activating sperms
- Bulbourethral glands: Secrete lubricating mucus

4. External Genitalia:
- Penis: Male copulatory organ for insemination

Q3. Explain the menstrual cycle in human females with hormonal regulation. 5M

Answer:
The menstrual cycle is approximately 28-day cycle with four phases:

1. Menstrual Phase (Day 1-5):
- Shedding of endometrium with bleeding
- Low levels of all hormones
- Menstruation occurs

2. Follicular/Proliferative Phase (Day 6-13):
- FSH from pituitary stimulates follicle development
- Growing follicle secretes estrogen
- Estrogen causes proliferation and thickening of endometrium
- Uterine glands lengthen

3. Ovulatory Phase (Day 14):
- High estrogen triggers LH surge from pituitary
- LH surge causes rupture of Graafian follicle
- Release of secondary oocyte (ovulation)

4. Luteal/Secretory Phase (Day 15-28):
- Ruptured follicle transforms into corpus luteum
- Corpus luteum secretes progesterone (and some estrogen)
- Progesterone maintains endometrium for implantation
- If fertilization doesn't occur, corpus luteum degenerates
- Progesterone and estrogen levels fall
- Endometrium breaks down → Menstruation begins

Hormonal Feedback:
- High estrogen → Inhibits FSH (negative feedback)
- High estrogen (mid-cycle) → Stimulates LH surge (positive feedback)
- Progesterone → Inhibits LH and FSH

Q4. Describe various contraceptive methods available for humans. 5M

Answer:
Contraceptive methods can be classified as follows:

1. Natural Methods:
- Periodic Abstinence: Avoiding coitus during ovulation period (day 10-17). High failure rate.
- Withdrawal: Male withdraws before ejaculation. High failure rate.
- Lactational Amenorrhea: Effective for 6 months after delivery during intense lactation.

2. Barrier Methods:
- Condoms: Latex sheaths covering penis/vagina. Protect from STIs. Disposable.
- Diaphragm/Cervical Cap: Cover cervix, block sperm entry. Reusable.
- Spermicides: Chemicals killing sperms. Used with barriers.

3. Intrauterine Devices (IUDs):
- Non-medicated: Lippes loop - increase phagocytosis
- Copper-releasing: CuT, Cu7 - suppress sperm motility
- Hormone-releasing: Progestasert, LNG-20 - prevent implantation. Effective for 5 years.

4. Oral Contraceptives (Pills):
- Contain progestogens ± estrogens
- Prevent ovulation by inhibiting FSH and LH
- Taken for 21 days, 7 days gap
- Emergency pills within 72 hours of unprotected coitus

5. Surgical Methods (Sterilization):
- Vasectomy: Cutting/tying vas deferens in males
- Tubectomy: Cutting/tying fallopian tubes in females
- Highly effective but irreversible

Ideal Contraceptive Qualities: User-friendly, easily available, effective, reversible, minimal side effects, doesn't interfere with sexual act.

Q5. What are Assisted Reproductive Technologies? Describe any three techniques. 5M

Answer:
Assisted Reproductive Technologies (ART) are techniques to help infertile couples have children.

Major ART Techniques:

1. IVF-ET (In Vitro Fertilization and Embryo Transfer):
- Ova from wife/donor and sperms from husband/donor collected
- Fertilization occurs in laboratory (in vitro) under controlled conditions
- Embryo formed (8-blastomere stage or blastocyst)
- Embryo transferred to uterus (IUT) or fallopian tube (ZIFT)
- Babies born are called "test-tube babies"
- First test-tube baby: Louise Joy Brown (1978)

2. GIFT (Gamete Intra-Fallopian Transfer):
- Ovum and sperms collected after inducing superovulation
- Both gametes transferred directly into fallopian tube
- Fertilization occurs naturally inside fallopian tube
- Embryo travels to uterus for implantation
- Difference from IVF: Fertilization occurs in vivo (inside body)

3. ICSI (Intra-Cytoplasmic Sperm Injection):
- Special type of IVF
- Single sperm directly injected into ovum cytoplasm
- Used when male has very low sperm count or motility
- Embryo formed in lab, then transferred to uterus
- Overcomes severe male infertility

Other techniques:
- AI (Artificial Insemination): Semen artificially introduced into vagina/uterus
- Surrogate mother: Embryo transferred to another woman who carries pregnancy
- Donor gametes: Used when couple cannot produce viable gametes