Biology: Topic-wise Test- 2 - NEET MCQ

The most important aspect of natural system of classification is direct observation of plants.therefore,it is based on morphological characters.

Answer:
Definition:
Related species that are reproductively isolated but morphologically similar are known as sibling species.
Explanation:
Here is a detailed explanation of each option and why the correct answer is B:
1. Allopatric:
- Allopatric refers to species that are geographically separated and are unable to interbreed due to physical barriers.
- Allopatric species are not morphologically similar, so this option is incorrect in this context.
2. Sibling:
- Sibling species are closely related species that have evolved from a common ancestor but are reproductively isolated.
- Sibling species are morphologically similar but cannot interbreed due to various factors such as differences in courtship behavior or genetic incompatibility.
- Therefore, this option is the correct answer.
3. Endemic:
- Endemic species are native or restricted to a specific geographic region.
- While endemic species can be reproductively isolated, they may not necessarily be morphologically similar to each other.
- Hence, this option is not the correct answer.
4. Sympatric:
- Sympatric species are species that live in the same geographic area and can potentially interbreed.
- In this case, the species mentioned are reproductively isolated, so they cannot be sympatric.
- Therefore, this option is incorrect.
In conclusion, the correct answer is B: Sibling species. These are related species that are reproductively isolated but morphologically similar.

Genera Plantarum is a publication of Swedish naturalist Carl Linnaeus (1707–1778). The first edition was issued in Leiden, 1737. The fifth edition served as a complementary volume to Species Plantarum (1753).

Dendrogram is based on:
Dendrogram is a graphical representation of the similarities and differences between different entities, such as species or samples. It is based on various taxonomic methods and data analysis techniques. The options given are:
A: Phenetic taxonomy
- Phenetic taxonomy is based on the overall similarity of organisms.
- It considers observable characteristics and phenotypes to group organisms.
- Dendrograms can be constructed based on phenetic taxonomy to show the relationships between different organisms.
B: Adansonian taxonomy
- Adansonian taxonomy, also known as natural classification, is based on multiple characteristics and overall similarity.
- It considers various taxonomic features, such as morphology, anatomy, and behavior, to classify organisms.
- Dendrograms can be constructed based on Adansonian taxonomy to visualize the relationships between different organisms.
C: Numerical taxonomy
- Numerical taxonomy is based on quantitative data and statistical analysis.
- It involves assigning numerical values to different characteristics of organisms and using mathematical algorithms to determine their relationships.
- Dendrograms can be constructed based on numerical taxonomy to represent the relationships between different organisms.
D: All of these
- The correct answer is D, as dendrograms can be constructed based on any of these taxonomic methods.
- Depending on the data available and the research question, different taxonomic methods may be used to construct dendrograms.
In conclusion, dendrograms are based on various taxonomic methods, including phenetic taxonomy, Adansonian taxonomy, and numerical taxonomy. These methods help in determining the relationships between different organisms and constructing graphical representations of their similarities and differences.

Set of diseases caused by actinomycetes:
- Actinomycetes are a group of bacteria that can cause various diseases in humans.
- The set of diseases caused by actinomycetes includes:
- Tuberculosis: Actinomycetes bacteria can cause tuberculosis, a contagious infection that primarily affects the lungs.
- Leprosy: Actinomycetes bacteria can also cause leprosy, a chronic infectious disease that mainly affects the skin, nerves, and mucous membranes.
- Diphtheria: Actinomycetes bacteria can cause diphtheria, a serious bacterial infection that affects the throat and can lead to difficulty breathing and other complications.
- Therefore, the correct answer is B: Tuberculosis, leprosy, and diphtheria.

To answer this question, we need to understand what Monera is and its different classifications. Here is a detailed solution:
Definition of Monera:
- Monera is a kingdom in the five-kingdom classification system of living organisms.
- It consists of prokaryotic organisms, which lack a true nucleus and membrane-bound organelles.
Classification of Monera:
Monera is divided into two main groups:
1. Archaebacteria:
- Archaebacteria are ancient bacteria that live in extreme environments such as hot springs, salt lakes, and deep-sea hydrothermal vents.
- They have unique cell walls and membranes that are different from other bacteria.
- Archaebacteria are considered to be the most primitive form of life on Earth.
2. Eubacteria:
- Eubacteria are the more common and diverse group of bacteria.
- They are found in various habitats, including soil, water, and the human body.
- Eubacteria have a wide range of metabolic capabilities and play essential roles in many ecological processes.
3. Cyanobacteria:
- Cyanobacteria, also known as blue-green algae, are a type of photosynthetic bacteria.
- They can perform photosynthesis and produce oxygen as a byproduct.
- Cyanobacteria are found in various environments, including freshwater, marine, and terrestrial habitats.
Answer:
- Monera includes all three groups mentioned above: Archaebacteria, Eubacteria, and Cyanobacteria.
- Therefore, the correct answer is D: All of these.
Summary:
- Monera is a kingdom in the five-kingdom classification system.
- It includes Archaebacteria, Eubacteria, and Cyanobacteria.
- Archaebacteria are ancient bacteria found in extreme environments.
- Eubacteria are more common and diverse bacteria.
- Cyanobacteria are photosynthetic bacteria also known as blue-green algae.

Best Method for Understanding the Phylogeny of Monerans
There are several methods for understanding the phylogeny of monerans, but one of the best methods is comparison of changes in the sequence of nucleotides in the RNA of ribosomes.
Explanation:
Using molecular homologies, scientists can compare the sequence of nucleotides in the RNA of ribosomes to understand the phylogeny of monerans. Here's why this method is considered the best:
- Highly conserved: Ribosomal RNA (rRNA) is highly conserved across different species, meaning that certain regions of rRNA remain relatively unchanged over long periods of evolutionary time. This allows scientists to compare the rRNA sequences of different monerans and identify similarities and differences.
- Slow evolutionary rate: The rate of evolution for rRNA is relatively slow compared to other genetic material. This slow rate allows scientists to analyze and compare rRNA sequences from a wide range of monerans and make conclusions about their evolutionary relationships.
- Universal presence: Ribosomes are essential cellular structures found in all living organisms, including monerans. This means that rRNA is present in all monerans and can be used to compare and analyze their phylogeny.
- Multiple regions of comparison: Scientists can compare different regions of rRNA, such as the small subunit (SSU) or the large subunit (LSU), to gain a more comprehensive understanding of moneran phylogeny. Each region provides different insights into evolutionary relationships.
- Availability of databases: There are extensive databases available that contain rRNA sequences from a wide range of monerans. Scientists can use these databases to compare and analyze sequences, making the process more efficient and accurate.
In conclusion, comparing changes in the sequence of nucleotides in the RNA of ribosomes is the best method for understanding the phylogeny of monerans due to the highly conserved nature of rRNA, its slow evolutionary rate, its universal presence in monerans, the ability to analyze multiple regions, and the availability of databases for comparison.

Answer:
Cyanobacteria are:
- Gram negative.
Explanation:
Cyanobacteria are a group of photosynthetic bacteria that are capable of producing oxygen through photosynthesis. They are found in various environments such as freshwater, marine, and terrestrial habitats. Here is a detailed explanation of the given options:
A: Gram positive:
- Gram-positive bacteria have a thick peptidoglycan layer in their cell wall that retains the crystal violet stain used in the Gram staining technique.
- Cyanobacteria, on the other hand, have a Gram-negative cell wall structure with a thin peptidoglycan layer surrounded by an outer membrane.
B: Gram negative:
- Cyanobacteria have a Gram-negative cell wall structure.
- This means that they have an outer membrane, a thin peptidoglycan layer, and an inner plasma membrane.
C: Saprophytic:
- Saprophytic organisms obtain their nutrients by decomposing dead organic matter.
- Cyanobacteria are not saprophytic because they are photosynthetic and use sunlight as a source of energy.
D: Chemosynthetic:
- Chemosynthetic organisms obtain energy by oxidizing inorganic compounds.
- Cyanobacteria are not chemosynthetic because they use sunlight for photosynthesis.
Therefore, the correct answer is B: Cyanobacteria are Gram negative.

Explanation:
The correct answer is B: The occurrence of branched chain lipids in the membranes.
Reasons:
- Archaebacteria are known for their ability to survive in extreme environments, including high or low pH conditions.
- The occurrence of branched chain lipids in the membranes is one of the key factors that enable archaebacteria to tolerate pH extremes.
- The branched chain lipids in the membranes help to stabilize the cell structure and maintain the integrity of the cell membrane.
- These lipids have unique properties that make them more stable and resistant to changes in pH compared to the lipids found in other types of bacteria.
- The branched structure of the lipids allows them to form a tight and stable membrane, which helps to protect the cell from damage caused by pH fluctuations.
- The presence of branched chain lipids in the membranes also enables the archaebacteria to adapt and survive in different pH environments, making them highly versatile organisms.
In summary, the occurrence of branched chain lipids in the membranes of archaebacteria is the key factor that enables them to tolerate pH extremes. These lipids provide stability and protection to the cell, allowing the archaebacteria to thrive in diverse pH conditions.

The Consumer-Decomposer Protists (Slime Moulds) and their Resemblance:

Cell wall composition of diatoms:
The cell wall of diatoms is composed of cellulose and silica. Here is a detailed explanation of this composition:
Cellulose:
- Diatoms have a primary cell wall made up of cellulose, which is a complex carbohydrate.
- Cellulose provides structural support and rigidity to the cell wall.
- It is a strong and flexible material that allows diatoms to maintain their shape and withstand environmental pressures.
Silica:
- Diatoms also have a secondary cell wall made up of silica, which is a mineral compound.
- Silica forms intricate patterns and structures, such as frustules, within the cell wall.
- These patterns are unique to each species of diatom and can be used for identification purposes.
- Silica adds an additional layer of protection to the cell and helps prevent deformation.
Importance of Cellulose and Silica:
- The combination of cellulose and silica in the cell wall gives diatoms their characteristic rigidity and durability.
- This enables diatoms to survive in various aquatic environments, including freshwater and marine habitats.
- The presence of silica also makes diatoms resistant to physical and chemical degradation.
- The intricate patterns formed by silica contribute to the diverse shapes and sizes observed in diatoms.
Summary:
The cell wall of diatoms is composed of cellulose and silica. Cellulose provides structural support, while silica adds rigidity and protection to the cell wall. This unique composition allows diatoms to thrive in different aquatic environments and maintain their intricate shapes.

Explanation:
Phytoalexins are substances that are produced by plants in response to microbial infection. They play a crucial role in the defense mechanisms of plants against pathogens. Here's a detailed explanation of why phytoalexins are secreted in the cell of the host plant due to infection caused by fungi:
1. Infection caused by fungi:
- Fungi are a type of microorganism that can cause various diseases in plants, such as fungal infections.
- When a plant is infected by fungi, it recognizes the presence of the pathogen and triggers a defense response.
- One of the defense mechanisms is the production and secretion of phytoalexins.
2. Role of phytoalexins:
- Phytoalexins are toxic compounds that are produced by plants in response to microbial attack.
- They act as chemical barriers to inhibit the growth and spread of pathogens, including fungi.
- Phytoalexins can directly inhibit the growth of fungi or interfere with their metabolic processes, ultimately reducing the severity of the infection.
3. Mechanism of phytoalexin production:
- When a plant detects the presence of fungal pathogens, it activates specific genes involved in phytoalexin biosynthesis.
- These genes are responsible for the production of enzymes that catalyze the synthesis of phytoalexins.
- The synthesized phytoalexins are then transported to the site of infection and accumulate in the infected cells, where they exert their antifungal activity.
4. Examples of phytoalexins:
- Different plants produce different types of phytoalexins, depending on the specific pathogen they are defending against.
- For example, isoflavonoids are phytoalexins produced by leguminous plants like soybeans in response to fungal infection.
- Other examples of phytoalexins include resveratrol in grapes, pisatin in peas, and camalexin in Arabidopsis.
Therefore, in the given options, the correct answer is D: Infection caused by fungi.

Majority of lichens are made of:
- Green algae and ascomycetes
Explanation:
Lichens are unique organisms that result from a mutualistic symbiotic relationship between a fungus and a photosynthetic partner, which is usually a green algae or a cyanobacterium. In most lichens, the photosynthetic partner is a green alga. The fungal partner belongs to the group of ascomycetes, which are fungi that produce spores in specialized structures called asci.
Here's a detailed explanation of why the majority of lichens are made of green algae and ascomycetes:
1. Mutualistic relationship: Lichens are formed when a fungus and a photosynthetic partner come together and form a mutually beneficial association. The fungus provides a protective environment and absorbs water and nutrients, while the photosynthetic partner provides food through photosynthesis.
2. Photosynthetic partner: The photosynthetic partner in most lichens is a green alga. Green algae are capable of photosynthesis, producing food (carbohydrates) using sunlight, water, and carbon dioxide. They provide the fungus with a source of energy and nutrients.
3. Fungal partner: The fungal partner in lichens belongs to the group of ascomycetes. Ascomycetes are a diverse group of fungi that produce spores in specialized sac-like structures called asci. These spores are responsible for the dispersal and reproduction of the fungus.
4. Structure of lichens: Lichens have a unique structure that reflects their dual nature. They consist of a thallus, which is the body of the lichen, and can have different forms such as crustose, foliose, or fruticose. The thallus is composed of fungal hyphae intertwined with the cells of the photosynthetic partner.
5. Other lichen associations: While the majority of lichens are made of green algae and ascomycetes, there are other combinations as well. Some lichens may have a cyanobacterium as the photosynthetic partner instead of a green alga. There are also lichens that have a fungal partner belonging to the group of basidiomycetes, which are fungi that produce spores on club-shaped structures called basidia. However, these combinations are less common compared to green algae and ascomycetes.
In conclusion, the majority of lichens are made of green algae and ascomycetes. This mutualistic partnership allows lichens to survive in diverse habitats and play important roles in ecological processes such as soil formation and nitrogen fixation.

Tikka disease of groundnut is due to Cercospora.
Explanation:
- Tikka disease is a common fungal disease that affects groundnut plants.
- The disease is caused by the fungus Cercospora arachidicola.
- The fungus infects the leaves of the groundnut plant, causing small, dark brown to black spots or lesions on the leaves.
- These spots are typically surrounded by a yellow halo, giving them a "tikka" or target-like appearance.
- Over time, the spots may enlarge and coalesce, leading to defoliation and reduced plant vigor.
- The disease can also affect the pods and stems of the plant.
- Cercospora spreads through spores that are released from infected plant debris and can be carried by wind or rain.
- Warm and humid conditions favor the development and spread of the disease.
- Crop rotation, proper sanitation, and the use of disease-resistant varieties are important management strategies for controlling Tikka disease in groundnut crops.
In summary, Tikka disease of groundnut is caused by the fungus Cercospora arachidicola, which infects the leaves, pods, and stems of the plant, leading to the formation of dark spots or lesions. Proper management practices are necessary to control the disease and minimize its impact on groundnut crops.

Coenocytic fungi which lack motile spores and produce zygospores belong to
Coenocytic fungi are a type of fungi that have a multinucleate cytoplasm without cell walls. They reproduce by producing zygospores, which are thick-walled resting spores. The group of fungi that exhibit these characteristics are known as Zygomycetes.
Explanation:
- Coenocytic fungi: These are fungi that have a multinucleate cytoplasm without cell walls. The lack of cell walls allows the cytoplasm to flow freely throughout the organism.
- Lack of motile spores: Motile spores are spores that are capable of moving on their own, usually propelled by flagella or cilia. Coenocytic fungi do not produce such motile spores.
- Zygospores: Coenocytic fungi reproduce by producing zygospores. Zygospores are thick-walled resting spores that are formed by the fusion of two compatible hyphae. They can survive in unfavorable conditions and germinate when conditions become favorable.
Therefore, based on the characteristics mentioned, coenocytic fungi that lack motile spores and produce zygospores belong to the group Zygomycetes (option B).

A possible mechanism that provides an answer to this question is the parasexual cycle. This is a process in which plasmogamy, karyogamy and haploidization takes place, but not in any particular place in the thallus nor at any specific period during its lifecycle.

Pollen grain is the first cell of the gametophyte. The microspore germinates in situ i.e., while within the microsporangium. Each microspore divides asymmetrically into a 2-cells: a smaller prothallial cell and a larger antheridialcell. The prothallial cell does not divide further while the antheridial cell divides into a smaller generative cell near the prothallial cell and a larger tube cell. Finally pollination takes place at 3-celled stage.

Some fresh water forms of algae are present in slow running waters for example Ulothrix, Cladophora, Oedogonium.

The non-flagellated thick-walled spores of Ulothrix are called Hypnospores. Let's break down the explanation into bullet points:
- Ulothrix is a genus of filamentous green algae found in freshwater environments.
- The reproductive structures of Ulothrix consist of non-motile, thick-walled spores.
- These spores are known as hypnospores and serve various functions in the life cycle of Ulothrix.
- Hypnospores are resistant to adverse environmental conditions, such as desiccation and extreme temperatures.
- They can remain dormant for extended periods and germinate when favorable conditions return.
- Hypnospores are involved in the survival and dispersal of Ulothrix, allowing the species to reproduce and colonize new habitats.
- Other options mentioned in the question are not correct:
- Aplanospores are non-motile spores that are not specifically associated with Ulothrix.
- Palmella stage refers to a stage in the life cycle of some algae where cells form a gelatinous mass.
- Akinetes are thick-walled spores produced by certain cyanobacteria, not Ulothrix.
Therefore, the correct answer is B: Hypnospores.

The main evolutionary features of alternation of generations from algae to flowering plants are:
1. Gradual elaboration of gametophyte:
- In algae, the dominant generation is the gametophyte, which produces gametes through mitosis.
- As we move from algae to flowering plants, there is a gradual elaboration of the gametophyte generation.
- This means that the gametophyte becomes more complex and specialized in its structure and function.
2. Gradual elaboration of sporophyte:
- In algae, the sporophyte generation is relatively simple and dependent on the gametophyte for nutrition.
- However, as we move towards flowering plants, there is a gradual elaboration of the sporophyte generation.
- The sporophyte becomes more independent and develops specialized structures for reproduction and dispersal, such as flowers and fruits.
3. Elimination of sporophyte:
- The elimination of sporophyte is not a feature of alternation of generations from algae to flowering plants.
- In fact, the sporophyte generation becomes more prominent and complex in flowering plants compared to algae.
4. Gradual elaboration of both gametophyte and sporophyte:
- This option is incorrect because it suggests that both the gametophyte and sporophyte undergo gradual elaboration, which is not true.
- While both generations do undergo changes, it is the sporophyte generation that shows a more significant elaboration.
Therefore, the correct answer is B: Gradual elaboration of sporophyte.

The sterile jacket around the sex organs is found in Bryophytes and Pteridophytes. Here is a detailed explanation:
Bryophytes:
- Bryophytes are non-vascular plants that include mosses, liverworts, and hornworts.
- They have a dominant gametophyte generation and a reduced sporophyte generation.
- The sex organs of bryophytes are called archegonia (female) and antheridia (male).
- The archegonia and antheridia are surrounded by a sterile jacket, which protects the sex organs and aids in fertilization.
Pteridophytes:
- Pteridophytes are vascular plants that include ferns, horsetails, and club mosses.
- They have a dominant sporophyte generation and a reduced gametophyte generation.
- The sex organs of pteridophytes are called archegonia (female) and antheridia (male).
- Similar to bryophytes, the archegonia and antheridia in pteridophytes are also surrounded by a sterile jacket.
Summary:
- The sterile jacket around the sex organs is a common feature in both bryophytes and pteridophytes.
- This jacket provides protection to the sex organs and helps in the process of fertilization.
- Therefore, the correct answer is A: Bryophytes and Pteridophytes.

Bryophytes are embryophytes that are non-vascular i.e., they have no xylem and phloem. Pteridophytes are vascular plants i.e., plants with xylem and phloem, that reproduce and disperse via spores.

The dominant phase in bryophyte is gametophyte while the dominant phase in pteridophyte is sporophyte. Bryophytes have no true roots while pteridophyte have true roots. Bryophytes have no vascular tissues while pteridophytes have vascular tissues.

Therefore, the correct answer is option D.

Plant Classification: Gymnosperms
Gymnosperms are a group of plants that possess certain characteristics such as producing spores, having vascular tissue, and producing seeds. However, they lack flowers. The correct group for the given plant description would be Gymnosperms.
Characteristics of Gymnosperms:
- Spore production: Gymnosperms produce spores as part of their reproductive cycle.
- Vascular tissue: Gymnosperms have specialized tissues for the transport of water, minerals, and nutrients throughout the plant.
- Seed production: Gymnosperms produce seeds, which are protected by structures such as cones.
- Lack of flowers: Unlike angiosperms (flowering plants), gymnosperms do not produce flowers.
Examples of Gymnosperms:
- Conifers: Pine trees, spruce trees, fir trees, and cypress trees are examples of gymnosperms.
- Cycads: Cycads are primitive gymnosperms with palm-like leaves.
- Ginkgo: The ginkgo tree is a unique gymnosperm known for its fan-shaped leaves.
In conclusion, the plant described in the question belongs to the group of gymnosperms. Gymnosperms produce spores, have vascular tissue, and produce seeds, but they lack flowers.

Explanation:
A unipinnate compound leaf can be differentiated from an ordinary branch with simple leaves based on the following characteristics:
A: The compound leaf has a terminal bud
- The compound leaf has a bud at the very end of the leaf stalk, known as the terminal bud.
- This bud is responsible for the growth and development of the leaf.
B: The compound leaf has axillary buds
- Along the leaf stalk of a compound leaf, there are small buds called axillary buds.
- Axillary buds have the potential to develop into new branches or leaves.
C: The branch has axillary buds in the axil of the leaves
- In contrast to the compound leaf, the ordinary branch has axillary buds.
- These axillary buds are located in the axil of the leaves, which is the angle between the leaf and the stem.
D: Both 2. and 3.
- The correct answer is D because both statements B and C are true.
- The compound leaf has axillary buds along the leaf stalk, and the ordinary branch has axillary buds in the axil of the leaves.
In summary, a unipinnate compound leaf can be differentiated from an ordinary branch with simple leaves by the presence of a terminal bud and axillary buds along the leaf stalk. The ordinary branch, on the other hand, has axillary buds in the axil of the leaves.

Petioles modified into tendrils in Clematis:
- Clematis is a plant species in which the petioles are modified into tendrils.
- Tendrils are slender, coiling structures that help the plant climb or attach to support.
- The modification of petioles into tendrils enhances the plant's ability to climb and reach sunlight.
- Clematis plants have long, flexible petioles that are capable of coiling and grasping onto nearby objects.
- These tendrils are sensitive to touch and can wrap around supports such as trellises, fences, or other plants.
- The modified petioles provide a means of attachment and support for the plant, allowing it to grow vertically and access more sunlight.
- This adaptation is beneficial for the plant's survival and growth in environments where climbing or attaching to supports is advantageous.
- Other examples of plants with similar modifications include Passiflora, Antigonon, and Gloriosa, but in this case, the correct answer is Clematis (option B).
Therefore, petioles are modified into tendrils in Clematis.

Why is ginger considered a stem and root?
Explanation:
Ginger is classified as both a stem and a root due to several characteristics that it possesses. Here's a detailed explanation:
1. Storage function:
- Ginger serves as a storage organ for the plant, storing food reserves that can be utilized during periods of dormancy or when nutrients are scarce.
2. Nodes and internodes:
- Ginger has distinct nodes and internodes, which are characteristic features of stems.
- Nodes are the points on the stem where leaves, branches, or flowers emerge, while internodes are the spaces between nodes.
- Ginger exhibits this stem-like structure, making it a stem.
3. Rhizome:
- The part of ginger that is typically consumed is the rhizome, which is an underground stem.
- Rhizomes grow horizontally beneath the soil surface and have nodes and internodes, further supporting the stem classification.
4. Non-green color:
- Unlike leaves, which are typically green due to the presence of chlorophyll, ginger has a pale yellowish-brown color.
- This non-green color is another characteristic commonly associated with stems rather than roots.
In conclusion, ginger is considered both a stem and a root because it exhibits stem-like characteristics such as nodes, internodes, and non-green color, while also serving as a storage organ like a root.

The correct answer is option A: Total stem parasite.
Here is a detailed explanation:
Cuscuta:
- Cuscuta, commonly known as dodder, is a parasitic plant that belongs to the family Convolvulaceae.
- It is a holoparasitic plant, meaning it is entirely dependent on its host plant for its nutrition.
- Cuscuta lacks chlorophyll and cannot photosynthesize, so it relies on its host for water and nutrients.
Types of Parasitism in Cuscuta:
Cuscuta exhibits the following characteristics that classify it as a total stem parasite:
1. Attachment:
- Cuscuta attaches itself to the stem of its host plant using specialized structures called haustoria.
- The haustoria penetrate the host plant's stem and establish a connection for nutrient absorption.
2. Dependency on Host:
- Cuscuta derives all its water, minerals, and nutrients from the host plant.
- It does not have its own root system and relies entirely on its host for sustenance.
3. Damage to Host:
- Cuscuta can cause significant harm to its host plant by depriving it of essential nutrients.
- It weakens the host's growth, reduces its productivity, and can ultimately lead to the death of the host plant.
4. Life Cycle:
- Cuscuta reproduces by producing seeds that germinate in the soil.
- Once the seedling emerges, it seeks out a suitable host plant to attach and begin its parasitic lifestyle.
In conclusion, Cuscuta is classified as a total stem parasite because it depends entirely on its host plant's stem for nutrition and lacks its own root system.

Velamen is a tissue found in aerial roots of some orchids.
Explanation:
- Velamen is a specialized tissue that is found in the aerial roots of certain orchids.
- This tissue acts as a protective layer and helps in absorbing and retaining water.
- The velamen tissue is made up of multiple layers of dead cells that are filled with air.
- It acts as a barrier against water loss and protects the delicate root tissues from desiccation.
- The velamen tissue also plays a role in the absorption of water and nutrients from the atmosphere.
- It has the ability to absorb moisture from the air and store it to support the orchid's growth and survival.
- Orchids that grow in epiphytic conditions, such as on trees or rocks, rely on the velamen tissue to obtain water and nutrients.
- The velamen tissue is easily recognizable as it appears white or silvery and has a spongy texture.
- This tissue is not found in parasites, saprophytes, or halophytes, but is specific to the aerial roots of certain orchids.
Therefore, the correct answer is C: Aerial roots of some orchids.

Explanation:
The graviperception (geotropic response) of roots is due to starch grains called statoliths. These statoliths play a crucial role in helping the root perceive the direction of gravity and grow in the appropriate direction. Among the given options, the cells in the root apex are responsible for housing these statoliths and facilitating the graviperception. Here is a detailed explanation:
Cells in the root apex:
- The root apex is the growing tip of the root and contains specialized cells.
- These cells contain starch grains or statoliths, which are dense and heavy.
- When the root is upright, these statoliths settle at the bottom of the cells due to gravity.
- This provides a signal to the plant about the direction of gravity.
- The plant can then adjust its growth accordingly, with the root growing towards gravity and the shoot growing against gravity.
Other options:
- Cells of the root cap: The root cap is responsible for protecting the delicate root tip, but it does not directly participate in graviperception.
- Cells of root hairs: Root hairs are responsible for nutrient absorption and anchoring the root, but they do not have a direct role in graviperception.
- Cells in the growing point: While the growing point is involved in the overall growth of the root, it is the cells in the root apex specifically that house the statoliths and facilitate graviperception.
Therefore, the correct answer is Option C: Cells in the root apex.