Biology: CUET Mock Test - 1 - CUET MCQ

Clones are organisms with the same genetic and morphological similarities. It can be carried out naturally and artificially. Asexual reproduction is an example of natural cloning. Artificial cloning is carried out in labs. In biotechnology cloning can refer to DNA fragments or cell copies.

Key Points

• During meiosis, which is the cell division responsible for the production of gametes (sperm and egg cells), the chromosome number is halved.
• This reductional division ensures that each gamete contains only one set of chromosomes, thus maintaining the species' chromosome number across generations.
• In the case of maize, whose meiocyte (a cell undergoing meiosis) contains 20 chromosomes, the number of chromosomes in each resulting gamete will be 10. This is because meiosis reduces the chromosome number by half.

Additional Information

• Option 2 (20 chromosomes): This would be the case if the cell division was mitotic, which maintains the original chromosome number, not meiotic.
• Option 3 (24 chromosomes): This option does not correlate with any known process of chromosome number reduction or duplication in maize gametogenesis.
• Option 4 (40 chromosomes): This would imply a doubling of the chromosome number, which is contrary to the reduction observed in meiosis.

Key Points

• Flowers are not an example of asexual reproduction. They are involved in sexual reproduction, which involves the fusion of male and female gametes.

Additional Information

• Conidia are asexual spores produced by fungi and are not involved in sexual reproduction processes.
• Buds, such as those seen in yeast or hydra, can develop into new individuals without the fusion of gametes, showcasing a form of asexual reproduction.
• Gemmules are involved in the asexual reproduction of sponges, allowing for the creation of new individuals without sexual reproduction.

Key Points

• Tapetum is the innermost layer of the microsporangium and plays a crucial role in nourishing the developing pollen grains.

Additional Information

• Epidermis is the outermost layer and provides protection but does not nourish the pollen grains.
• Endothecium is the layer next to the epidermis, involved in the dehiscence of anther to release pollen grains.
• Middle layer is relatively less significant in the direct nourishment of developing pollen grains.

The correct option is A - III, B - IV, C - I, D - II.

Key Points

• Albuminous seed matches with Castor (A - III).
  • Albuminous seeds contain endosperm, a nutritive tissue that provides nourishment to the developing embryo. Castor seeds are an example of albuminous seeds as they retain their endosperm until germination.
• Parthenocarpic fruit matches with Banana (B - IV).
  • Parthenocarpy refers to the development of fruits without fertilization, leading to seedless fruits. Bananas are a common example of parthenocarpic fruits, as they develop without seed formation.
• Non-albuminous seed matches with Groundnut (C - I).
  • Non-albuminous seeds do not have endosperm at the time of germination. The endosperm is completely consumed during the seed's development. Groundnut seeds are an example of non-albuminous seeds as they lack endosperm when they germinate.
• False fruit matches with Apple (D - II).
  • False fruits, or pseudocarps, are fruits where parts other than the ovary contribute to the flesh of the fruit. In apples, the edible part is derived not from the plant's ovaries but from the receptacle that holds the ovaries, making apples false fruits.

Therefore, the correct pairing is:
A - III: Albuminous seed - Castor
B - IV: Parthenocarpic fruit - Banana
C - I: Non-albuminous seed - Groundnut
D - II: False fruit - Apple

Key Points

• Spermiogenesis is the correct term for the transformation of spermatids into spermatozoa. This process involves the maturation of spermatids into fully functional, motile sperm cells.

Additional Information

• Spermatogenesis is a broader process that encompasses the entire cycle of the development of sperm cells, starting from the spermatogonial stem cells to the final spermatozoon.
• Spermiation is the process at the end of spermatogenesis where mature spermatozoa are released from the Sertoli cells into the lumen of the seminiferous tubules.
• Spermation is not a recognized term in the context of spermatogenesis or the maturation of sperm cells.

Concept:

• The transfer of pollen grains from the anther to stigma is known as pollination.
• Pollination is essential for fertilization in plants.
• There are two types of pollination- self-pollination, and cross-pollination.

Explanation:

• Pollination occurs by different pollinating agents such as wind, water, birds, insects, and bats.
• Pollination in water hyacinth occurs by insects. Pollination by insects is known as entomophily.
• They are pollinated by insects as they have colorful flowers.
• Wind pollination is known as anemophily and it occurs in water lilies.
• They produce many pollens, so they are pollinated by winds.

So, the correct answer is option 3.

The correct answer is Only III

• Polyembryony refers to the occurrence of more than one embryo in a single seed.
• Polyembryony is derived from the Greek words "poly," meaning many, and "embryo," referring to the early stage of development in a seed. It literally means the occurrence of multiple embryos within a single seed.
• In polyembryony, each embryo arises from a separate fertilization event or from the development of multiple embryos from a single fertilized egg cell.

There are two main types of polyembryony:-

• True Polyembryony: In this type, multiple embryos develop from different fertilized egg cells or zygotes. Each embryo has its own genetic makeup and develops independently within the seed.
• Adventitious Polyembryony: In this type, multiple embryos develop from cells of the nucellus or integuments surrounding the ovule. These embryos are genetically identical to the maternal plant and are considered clones.

Polyembryony is observed in various plant species, including citrus fruits, mangoes, pineapples, and some gymnosperms.

• In citrus fruits, such as oranges and lemons, polyembryony is a common phenomenon. Multiple embryos can develop within a single seed, resulting in seedlings with varying genetic characteristics.

Conclusion
Therefore, the correct answer is Only III.

Concept:

• Embryo formation takes place after the fertilization of egg cell by the male gamete.
• Flowering plants have the unique characteristic feature of double fertilization.
• Each pollen grain has 2 male gametes and both take part in fertilization.
• Double fertilization involves 2 processes:
  • Syngamy - It is the fusion of one male gamete with the egg cell to produce a zygote that later develops into embryo.
  • Triple fusion - It is the fusion of the 2nd male gamete with the 2 polar nuclei of the embryo sac to produce the endosperm.
• Therefore, double fertilization can be summed up as:

1st Male gamete (n) + Egg (n) → Zygote (2n)
2nd Male gamete (n) + 2 Polar nuclei (n) → Endosperm (3n)

Important Points

• The endosperm develops before the embryo to provide nutrition to the developing embryo.
• The embryo starts developing at the micropylar end of the embryo sac, where the egg cell was positioned.
• Most zygotes start dividing after partial development of endosperm, in order to assure nutrition to the embryo.
• The process of embryo development is known as embryogeny.
• The early stages of embryogeny are similar in dicots and monocots.
• In a dicot plant, the zygote first gives rise to the proembryo.
• The proembryo then subsequently forms the globular embryo, which is round in shape.
• Then the heart-shaped embryo is formed and the rest of the embryo sac starts degenerating.
• Lastly the mature embryo is formed.
• Thus, the correct sequence of embryo development is:

Proembryo → Globular embryo → Heart-shaped embryo→ Mature embryo

Additional Information

• A typical dicot embryo consists of an embryonal axis and two cotyledons.
• The part of embryonal axis above the cotyledons is called epicotyl.
• The epicotyl terminates at the plumule, which later gives rise to the stem.
• Plumule is covered by the coleoptile.
• The portion below the cotyledons is the hypocotyl, which terminates at the radicle.
• Radicle gives rise to the root and is protected by coleorhiza.

The correct answer is Gastrulation

• Gastrulation is a key developmental process that occurs during the early stages of embryogenesis, following fertilization and cleavage.
• During gastrulation, the single-layered blastula undergoes extensive rearrangement and differentiation to form the three primary germ layers: ectoderm, mesoderm, and endoderm.
• The ectoderm gives rise to structures such as the nervous system, skin, and teeth enamel.
• The mesoderm forms tissues including muscles, bones, blood vessels, and the urogenital system.
• The endoderm contributes to the development of the digestive tract, respiratory tract, liver, and pancreas.
• Gastrulation involves complex cellular movements, including invagination, involution, and epiboly, which result in the formation of the three germ layers and establish the basic body plan of the embryo.

• Fertilization is the process of fusion between a sperm cell and an egg cell, leading to the formation of a zygote.
• Cleavage ( refers to the rapid cell divisions that occur in the early embryo, leading to the formation of a multicellular blastula.
• Organogenesis is the process by which the germ layers differentiate and give rise to specific organs and organ systems during later stages of embryonic development, following gastrulation.

Conclusion
The process in which the three germ layers form is called Gastrulation.

The correct answer is option 2.

Concept:

• There are published records of all the species discovered so far.
• These records make it possible to estimate how many species are there.

Explanation

• Estimation of the number of species on Earth
  • As per the estimates of the International Union for Conservation of Nature and Natural Resources (IUCN) (2004), the total number of animal and plant species described so far are more than 1.5 billion.
  • Estimates vary widely and most of them are guesses based on certain assumptions.
• Extrapolation of obtained data to estimate the species number
  • As per biologists, a large proportion of species have to be discovered in the tropics.
  • To make an estimate biologists use a statistical comparison of tropical - temperate species richness of an exhaustively studied group of insects and extrapolate the obtained ratio to another group of plants and animals for coming up with a gross estimate of the total number of species on the Earth.
  • Some extreme estimates range between 20 to 50 million species.
• An estimate by Robert May
  • However, the more scientific estimate was given by Robert May.
  • According to his estimate, there are 7 million species on Earth.

So, the correct answer is option 2.

The fusion of a haploid male (23 chromosomes) and a haploid female gamete (23 chromosomes) produces a diploid (46 chromosomes) egg or a zygote. This process of reproduction is known as sexual reproduction.

Gametogenesis refers to the formation of the gametes. In sexual reproduction formation of gametes is very important since an offspring is formed only after the fusion of the gametes. Gamete transfer refers to bringing the 2 gametes together.

Sexual reproduction is divided into 3 events. Pre-fertilization, fertilization and post-fertilization events. Pre fertilization is the events occurring before fusion of gametes (gametogenesis), fertilization is the fusion of gametes to form zygote and post-fertilization are the events occurring after zygote formation.

Conidia are non-motile fungal spores that are produced singly or in chains by constriction of tips of conidiophores and are dispersed by wind. Zoospores are motile fungal spores. Gemmules are reproductive structures of sponges and nodes are just a site on the stem from where the new plant arises in rhizomes (vegetative propagation).

The phase when it is growing is known as the juvenile phase or the vegetative phase (in plants). The phase after that when the reproductive organs in the organism matures is known as the reproductive phase. Senescence is the phase when the plant starts deteriorating as it grows old and finally dies.

Water hyacinth

The water hyacinth, also known as Eichhornia crassipes, is referred to as the "terror of Bengal" because it is an invasive aquatic plant that has caused significant environmental and economic problems in Bengal and other regions. The plant grows and reproduces rapidly, covering the surface of water bodies, which negatively impacts native species, blocks sunlight and oxygen, and impedes water transportation. Efforts to control and remove water hyacinth have proven challenging and costly.

Organisms having haplontic lifecycles, zygote divides by meiosis to form haploid spores that grow into haploid individuals. Formation of zygote forms the vital link, ensuring continuity of the species.

It is difficult to clearly distinguish between the different phases in perennial plants. Some plants exhibit unusual flowering phenomena. Some plants flower every year, there are some that flower every 10 years and some plants flower every 50 years. Neelakurinji is a flowering plant that flowers every 12 years.

Male gamete is called antherozoid or sperm. They are called so in heterogametes. The two gametes produced are morphologically distinct types. The female gamete is called egg or ovum.

Embryogenesis is the process of embryo formation from a zygote. It undergoes mitosis and cell differentiation in this process. Cell differentiation helps in categorizing cells into specialized tissues.

Monocarpic plants flower only once in its lifetime. They die after flowering. Annuals like marigold, wheat, paddy, biennials like radish, perennials like Bambusa tulda which flowers every 50-100 years, fruits and dies.

Stamens are the male organs of a flower. Flowers maybe unisexual (either staminate or pistillate). In staminate plants only the male part, that is the stamen, is present and in the pistillate plants only the female part is present (ovaries). In bisexual plants, both are present.

Animals are categorized into 2 types of–oviparous and viviparous. Oviparous animals are those animals in which zygote development takes place outside the body. Reptiles and birds are examples of oviparous animals.

In suckers the lateral branches arise from basal and underground portions of the main stem. They grow horizontally underground and the leafy shots arise from the soil. For example, bananas.

 Polycarpic plants are those that flower repeatedly, which means they do not die after flowering once. Examples are perennials like apple, mango and perennial flowers like china rose, it flowers throughout the year.

A plant having both reproductive organs in the same plant is known as monoecious plants. It may also be known as homothallic conditions. Dioecious plants are those which have only one reproductive organ, also known as unisexual plants. Another word for dioecious plants is heterothallic.

Animals are categorized into 2 types of–oviparous and viviparous. Viviparous animals are those animals in which zygote development takes place within the body itself. Mammals are a very good example for viviparous reproduction.

Tulip is an example of a bulb. It is a vegetative propagation by underground stems. They have more than one terminal buds. Another very common example is the onion. Oxalis is and example of a runner and the other 2 are examples of vegetative propagation by leaves.

There are 3 phases in a life cycle.
(i) Juvenile phase/ vegetative phase: period from birth to maturation of reproductive systems.
(ii) Reproductive phase: period when the reproductive systems have matured and ready to produce offspring.
(iii) Senescence: period when the organism starts growing old and starts degrading.