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Sexual Reproduction (Plants & Humans) Quiz
Sexual Reproduction (Plants & Humans) - Set 1
1. In an angiosperm, the innermost wall layer of the microsporangium that provides nourishment to the developing pollen grains is called:
The microsporangium has four wall layers: epidermis, endothecium, middle layers, and tapetum. The **Tapetum** is the innermost layer and its primary function is to nourish the developing pollen grains.
2. If the haploid number of chromosomes in a flowering plant is $n = 12$, what will be the ploidy and chromosome number of the endosperm after triple fusion?
Triple fusion involves the fusion of one male gamete ($n$) with two polar nuclei (forming a secondary nucleus, $2n$). The resulting Primary Endosperm Nucleus (PEN) is triploid ($3n$). If $n=12$, then $3n = 3 \times 12 = 36$.
3. Which part of the mammalian sperm contains a high concentration of mitochondria to provide energy for motility?
The **Middle piece** of the sperm contains numerous mitochondria, which produce energy in the form of ATP for the movement of the tail, facilitating sperm motility.
4. A mature embryo sac in a typical angiosperm is described as:
At maturity, a typical angiosperm embryo sac (Polygonum type) consists of 7 cells (3 antipodals, 2 synergids, 1 egg cell, and 1 large central cell) but contains 8 nuclei because the central cell has two polar nuclei.
5. The surge of which hormone is directly responsible for the process of ovulation in the human menstrual cycle?
Both LH and FSH attain a peak level in the middle of the cycle (about $14^{th}$ day). Rapid secretion of **LH** leading to its maximum level during the mid-cycle (LH surge) induces the rupture of Graafian follicle and release of ovum (ovulation).
6. The hard outer layer of the pollen grain called exine is composed of a highly resistant organic material known as:
**Sporopollenin** is one of the most resistant organic materials known. It can withstand high temperatures and strong acids and alkalies. No enzyme that degrades sporopollenin is so far known.
7. In human females, where does the fertilization of the ovum by the sperm normally occur?
Fertilization in humans takes place in the fallopian tube, specifically at the **ampullary-isthmic junction** (or simply the ampulla).
8. What is the function of Filiform apparatus located at the micropylar part of the synergids?
The synergids have special cellular thickenings at the micropylar tip called the **filiform apparatus**, which play a crucial role in guiding the pollen tubes into the synergid.
9. Leydig cells, found in the interstitial spaces of the testes, are responsible for the secretion of:
**Leydig cells** (interstitial cells) synthesize and secrete testicular hormones called androgens, primarily testosterone.
10. Which of the following depicts the correct pathway of sperm transport in the male reproductive system?
The seminiferous tubules open into the **rete testis**, which leads to **vasa efferentia**. These open into the **epididymis** located along the posterior surface of each testis, which then leads to the **vas deferens**.
11. Double fertilization is a unique characteristic of angiosperms. It involves:
**Double fertilization** involves two types of fusion in the embryo sac: Syngamy (fusion of one male gamete with the egg to form a zygote) and Triple Fusion (fusion of the second male gamete with two polar nuclei to form the primary endosperm nucleus).
12. In human embryonic development, the blastocyst becomes embedded in the layer of the uterus called the:
Implantation occurs when the blastocyst becomes embedded in the **endometrium**, the innermost glandular layer of the uterus.
13. Persistent nucellus in some seeds (like Black Pepper and Beet) is known as:
In some seeds, remnants of the nucellus are persistent. This residual, persistent nucellus is called the **perisperm**.
14. The process of formation of a mature female gamete (ovum) is called oogenesis. At which stage is oogenesis initiated in human females?
Oogenesis is initiated during the **embryonic development** stage when a couple of million gamete mother cells (oogonia) are formed within each fetal ovary; no more oogonia are formed and added after birth.
15. Cleistogamous flowers are those which:
**Cleistogamous** flowers do not open at all. In such flowers, the anthers and stigma lie close to each other, ensuring autogamy (self-pollination).
16. The first milk produced by the mother during the initial few days of lactation, which contains antibodies ($IgA$) essential for the newborn, is:
The milk produced during the initial few days of lactation is called **colostrum** which contains several antibodies absolutely essential to develop resistance for the new-born babies.
17. If a pollen grain has $20$ chromosomes, how many chromosomes will be present in the generative cell and the tube cell respectively?
Both the generative cell and the tube cell are formed by the mitotic division of the haploid microspore ($n$). Therefore, they both contain the same number of chromosomes as the pollen grain. If the pollen grain is $n=20$, both cells have $20$ chromosomes.
18. Which of the following is NOT a function of the placenta in humans?
The placenta facilitates the supply of oxygen and nutrients and the removal of wastes. It also acts as an endocrine tissue (secreting hCG, hPL, estrogens, progesterones). **Oxytocin** is secreted by the maternal posterior pituitary, not the placenta.
19. The part of the ovary that acts as a temporary endocrine gland after ovulation and secretes progesterone is the:
After ovulation, the remaining parts of the Graafian follicle transform into the **corpus luteum**. The corpus luteum secretes large amounts of progesterone which is essential for maintenance of the endometrium.
20. Wind pollinated (anemophilous) flowers usually have:
Wind pollination requires the pollen grains to be **light and non-sticky** so that they can be transported in wind currents. They often possess well-exposed stamens and large feathery stigmas to trap air-borne pollen grains.
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