RBSE Solutions Class 11 Biology Chapter 39 Environmental Factors

RBSE Class 11 Biology Chapter 39 Multiple Choice Objective Questions

Question 1. Which of the following factor primarily decides the vegetation of a region-
(a) Climatic
(b) Topographical
(c) Biotic
(d) Edaphic
Answer: (a) Climatic
In simple words: The main factor that determines what kind of plants grow in a specific area is the climate, including things like temperature and rainfall.

🎯 Exam Tip: Remember that climate (long-term weather patterns) is the overarching factor influencing plant life in a region.

Question 2. Most suitable for plant growth -
(a) Sand soil
(b) Loam soil
(c) Clay soil
(d) Gravel
Answer: (b) Loam soil
In simple words: Loam soil is the best type of soil for plants to grow in because it has a balanced mix of sand, silt, and clay, which provides good air and water for roots.

🎯 Exam Tip: Good soil for plant growth needs a balance of water retention and drainage, which loam soil provides due to its mixed composition.

Question 4. Root cap is normally absent in -
(a) Hallophytes
(b) Xerophytes
(c) Hygrophytes
(d) Mesophytes
Answer: (c) Hygrophytes
In simple words: Plants that live in water or very wet environments, called hygrophytes, usually do not have root caps because their roots don't need protection while pushing through soil.

🎯 Exam Tip: Root caps protect root tips as they grow through soil; in water-filled environments, this protection is less necessary.

Question 5. Many hygrophytes disappear from the pond during summer because -
(a) More light is present
(b) Plants migrate towards shadow places
(c) Plants die because of evaporation
(d) CO2 concentration in water is reduced due to high temperature. As a result plants couldn't perform sufficient photosynthesis.
Answer: (d) CO2 concentration in water is reduced due to high temperature. As a result plants couldn't perform sufficient photosynthesis.
In simple words: During summer, ponds get warmer, which means there is less carbon dioxide gas dissolved in the water. Water plants (hygrophytes) need this carbon dioxide for making their food, so many cannot survive and disappear.

🎯 Exam Tip: Remember that gas solubility in water decreases as temperature increases, impacting aquatic life that relies on dissolved gases.

RBSE Class 11 Biology Chapter 39 Very Short Answer Questions

Question 1. What is PAR?
Answer: PAR stands for Photosynthetically Active Radiation. It is the specific part of sunlight that plants can use for the process of photosynthesis, where they make their food.
In simple words: PAR is the visible light from the sun that plants use to grow and create their own food.

🎯 Exam Tip: Define PAR clearly and mention its role in photosynthesis.

Question 2. What is Lapse rate.
Answer: Drosera, Nepenthes, and Utricularia are some types of plants.
In simple words: Drosera, Nepenthes, and Utricularia are names of certain plants.

🎯 Exam Tip: Be precise with definitions. The lapse rate refers to how air temperature changes with altitude in the atmosphere.

Question 4. Write botanical names of four plants having root pneumatophores (spaces)
Answer: Four plants that have root pneumatophores are Rizophora, Avicennia, Ceriops, and Nypct. These are special roots that help plants breathe in waterlogged or muddy soils.
In simple words: Rizophora, Avicennia, Ceriops, and Nypct are plants with special roots called pneumatophores, which help them get air.

🎯 Exam Tip: When listing botanical names, ensure correct spelling. Pneumatophores are a key adaptation for plants in mangrove or swampy environments.

Question 5. What are phreatophytes?
Answer: Phreatophytes are plants with very long roots that grow deep down into the soil to reach the "phreatic zone," which is the area where the soil is completely full of water. This allows them to get the water they need.
In simple words: Phreatophytes are deep-rooted plants that get their water from underground areas where the soil is always saturated.

🎯 Exam Tip: Emphasize "deep roots" and "phreatic zone" when defining phreatophytes.

Question 6. What are malacophyllous? What is the reason of their fleshy nature.
Answer: Malacophyllous plants are those that have thick, fleshy leaves. They have these fleshy leaves because they contain special tissues designed to store a lot of water.
In simple words: Malacophyllous plants have soft, thick leaves because these leaves are made to store water.

🎯 Exam Tip: Connect the term "malacophyllous" with "fleshy leaves" and "water storage" as key characteristics.

RBSE Class 11 Biology Chapter 39 Short Answer Questions

Question 1. Differentiate season & weather.
Answer: Climate is the usual weather pattern of a place over many years, including factors like average temperature and rainfall. Weather, however, describes the condition of the atmosphere at a specific time and place, which can change daily or weekly. So, weather is short-term, while climate refers to long-term patterns.
In simple words: Weather is what happens outside right now, like sun or rain today. Climate is the usual kind of weather a place has over a very long time, like hot summers and cold winters.

🎯 Exam Tip: Clearly distinguish between the timeframes: weather is short-term (daily/weekly), and climate is long-term (years/seasons).

Question 2. Differentiate Heliophytes & Sciophytes.
Answer: Heliophytes, also known as photophilous or heliphelous plants, are types of plants that require a lot of bright sunlight to grow well. Good examples of these plants include sunflowers, amaranthus, and populus trees.
Sciophytes are different; these plants thrive and grow best in areas with less light or in shady conditions. They do not need strong, direct sunlight to develop.
In simple words: Heliophytes love bright sun to grow, like sunflowers. Sciophytes like shade and grow well in less light.

🎯 Exam Tip: When differentiating, define both terms clearly and provide characteristic examples for each type of plant.

Question 3. Explain types & formation of humus.
Answer: Humus is also called soil organic matter and is very important for soil fertility. It forms when dead plants, animals, and their waste break down in the soil. Earthworms, bacteria, and fungi help in this process by consuming the organic material. This formation of humus is called humification. When humus further breaks down into simpler mineral salts, it's called mineralization.
Humus comes in two main types:

• Mor humus: This is a raw type of humus that has very few mineral salts, microorganisms, or animals.
• Mull humus: This is a more developed, granular type of humus that contains many microorganisms and earthworms, making it very fertile.

In simple words: Humus is dark, rich soil made from decayed plants and animals. It helps soil stay healthy. There are two kinds: raw (mor humus) and mature (mull humus).

🎯 Exam Tip: Remember to explain both the formation process (humification, mineralization) and the two main types of humus with their key differences.

Question 4. Write short notes on (a) Vernalization (b) Photoperiodism
Answer:
(a) Vernalization – This is a process where some plants need to be exposed to a long period of cold temperatures, like winter, to start flowering. It can also be achieved artificially by treating seeds with low temperatures. Oxygen is necessary for this process. Scientists believe that during vernalization, a compound called Vernalin forms, which then converts into Florigen or gibberellin, hormones responsible for initiating flowering.
(b) Photoperiodism – This describes how the length of daily light or darkness affects when plants flower and produce fruit. The term was first used by Garner & Allard in 1920. Plants are classified into three types based on their daily light requirements for flowering:
1. Long-day plants (LDP): These plants flower when the days are long.
2. Short-day plants (SDP): These plants flower when the days are short.
3. Day-neutral plants (DNP): These plants flower regardless of the day length.
In simple words: (a) Vernalization means plants need cold weather to start flowering. (b) Photoperiodism means how the amount of light in a day affects when plants flower or make fruit.

🎯 Exam Tip: For vernalization, remember "cold temperature exposure" and "flowering initiation." For photoperiodism, focus on "day length" and its "effect on flowering," along with the three plant types.

RBSE Class 11 Biology Chapter 39 Essay Type Questions

Question 1. Give a brief account of climatic factors which affect the plants.
Answer:
Climatic factors include various environmental elements such as light, temperature, air, water, humidity, and different gases. The study of these climatic factors is known as climatology. These factors play a very important role in determining how plants grow and where they are distributed.
**Light:** Sunlight is the only natural source of light. The visible part of solar radiation, ranging from 390 nM to 760 nM, is known as Photosynthetically Active Radiation (PAR). Light energy affects organisms in several ways:
(A) Wavelength of Light- Different colors in the visible light spectrum have different wavelengths. Photosynthesis, the process by which plants make food, happens most effectively in red light (650 to 760 nM) and then in blue light (430 to 470 nm). It is almost non-existent in green light (500 to 560 nm). Carotenoids absorb the middle part of the spectrum, transferring this energy to chlorophyll. Red light helps plants build carbohydrates, while blue light aids in protein synthesis. Although UV rays can be harmful, they help plants produce anthocyanin pigment. Certain purple sulfur bacteria use infrared and UV radiation for photosynthesis.
(C) Duration of Light or Photoperiodism - This refers to how the length of daily light or the day-night cycle affects the flowering and fruiting of plants. The term "photoperiodism" was first used by Garner and Allard in 1920. Based on the amount of daily light required for flowering, plants are classified into three types:
1. Long-day plants (LDP)
2. Short-day plants (SDP)
3. Day-neutral plants (DNP)
2. Effect on Transpiration - Light controls when stomata (small pores on leaves) open and close for gas exchange. Stomata open during bright light, which increases transpiration (the release of water vapor). The rate of transpiration influences how much water a plant absorbs and how quickly sap moves up the plant.
3. Effect on Respiration & Plant growth - As light intensity increases, the rate of respiration in many plants also increases. This depends on factors like the cell membrane's permeability and the protoplasm's thickness. Light also affects seedling growth, seed germination, bud development, and the overall growth of shoots. Seedlings that do not receive enough light turn yellowish, a condition called etiolation. Light is crucial for the production of florigen hormone and other plant growth hormones.
4. Effect of Light on Plant distribution - Light is a major factor in where plants are found locally and how different layers of vegetation form. In aquatic environments (like lakes and oceans), light determines where plants grow. This leads to the formation of different zones, such as the Littoral, Lacustrine (or Limnetic), and Profundal zones.
5. Effect of Light on Internal structure of Plants - Light primarily affects the internal structure of leaves. In dicotyledonous plants, the top (dorsiventral) leaves show differences between their columnar tissue and spongy parenchyma because light is not evenly distributed. However, in monocotyledonous plants, both sides of the isobilateral leaves do not show such variations in mesophyll because light is evenly distributed, and all cells are similar in shape.
6. Effect of Light on Aquatic system - In aquatic ecosystems (such as ponds, lakes, and oceans), light regulates plant distribution. The availability and intensity of light control vital activities. In deep aquatic systems, light levels determine the types and populations of producers and consumers. For example, phytoplankton are found in the limnetic zone, while benthic animals live at the bottom.
In simple words: Climatic factors like light, temperature, water, and air greatly impact plants. Light affects how plants grow, when they flower, and even what parts of the leaf look like. Different light colors and how long the day is (photoperiodism) are also important. Too much or too little light affects how much water plants lose (transpiration), how they breathe (respiration), and their overall growth. Light also decides where plants live, especially in water, and how their cells are shaped inside.

🎯 Exam Tip: For essay questions on climatic factors, organize your answer by specific factors (light, temperature, water) and discuss their various effects on plant physiology, growth, and distribution with clear examples.

Question 2. How the Edaphic factors affect the plants?
Answer: Edaphic factors are about how soil affects plants. Soil is the topmost layer of Earth's crust where plants grow. It's a complex mix of minerals and organic materials that have broken down. The study of soil is called pedology. Soil forms from the interaction of parent rocks, the environment, living organisms, and time. This process of soil formation from weathered rocks is known as pedogenesis. Rocks are made of minerals that constantly break down, a process called degradation.
Three main factors help in soil formation:
1. Physical factors: These include air, rainfall, temperature, and landslides.
2. Chemical factors: These involve processes like hydrolysis, oxidation, catabolism, hydration, and carbonization.
3. Biological factors: Living things like moss, blue-green algae, and animals contribute to soil formation.
Soil formation is a continuous but very slow process. Based on how they form and where their minerals come from, soils are of two main types:
(a) Residual soil: This is soil that stays in the same place where it formed.
(b) Transported soil: This is soil that has been moved from other places by different methods. There are four types:

• Alluvial soil: This soil is carried by water.
• Glacial soil: This soil is carried by glaciers.
• Colluvial soil: This soil is moved by Earth's gravity.
• Aeolian soil: This soil is carried by air.

**Soil Profile:**
A soil profile shows the distinct layers of soil, called horizons. Each layer runs roughly parallel to the soil surface and has its own unique properties. A soil profile is a vertical cross-section of these layers.
1. Horizon 'A' (Topsoil): This is the uppermost layer, also known as topsoil. It allows plants to grow and is formed by the breakdown of rocks and the activities of organisms. It is rich in humus and is dark brown.
2. Horizon 'B' (Subsoil): This layer is below the topsoil, also called subtopsoil. It is lighter brown and denser than topsoil. It contains few or no living organisms, but has fine rock particles and soluble minerals. It stores rainwater and acts as a water reservoir, supplying water to the topsoil through capillary action.
3. Horizon 'C' (Substratum): This is the lowest layer of the soil profile, which is less important for life. Long plant roots can sometimes reach this layer, which is followed by hard rocks.
**Composition of soil:**
Normally, garden soil consists of four main components:
1. Mineral components (40% by volume)
2. Soil organic matter (10% by volume)
3. Soil water (25% by volume)
4. Soil air (25% by volume)
**1. Mineral Components & Soil texture:**
Minerals come from rocks, and their particle size affects soil properties. Chemically, gravel and sand are inert, made mostly of aluminum and silicon oxides. The relative amounts of mineral particles of various sizes determine the soil texture. Pebbles and gravel are not usually included in textural classifications.
The soil texture determines how much water it can hold, its nutrient content, and how well plants grow. Based on the relative ratio of rock particles, soil is classified into six types:

• Sandy soil: Contains mostly sand particles. It has good air circulation but holds less water and nutrients.
• Clay soil: Contains mostly clay particles. It has high water-holding capacity but poor air circulation, making it less suitable for most plants.
• Loam soil: Contains an equal mix of silt and clay. It has moderate air circulation and water-holding capacity, making it ideal for plant growth.
• Sandy loam soil: A type of loam soil with more sand particles.
• Silt loam soil: A type of loam soil with more silt particles.
• Clay loam soil: A type of loam soil with more clay.

**2. Soil Organic Matter (Humus):**
Also known as humus, soil organic matter is essential for soil fertility. It is formed by the decaying organic material from dead organisms, plants, animals, and their waste. Earthworms and microorganisms like bacteria and fungi use humus as food. The formation of humus is called humification, and its conversion into mineral salts is called mineralization. Humus has two main types:
(a) Mor humus: This is raw humus, with fewer mineral salts and very few microorganisms or animals.
(b) Mull humus: This is a granular and mature humus that has many microorganisms and earthworms.
**3. Soil Water:**
Rain is the main source of soil water. After heavy rain, some water flows away as runoff water and is not easily available to plants. Some water moves deeper due to gravity, reaching the water table; this is called gravitational water and is also not easily available to plants. A part of the rainwater occupies the spaces between colloidal soil granules or forms a thin layer around them.
**Soil water holding or Field Capacity (FC):** Field capacity is the amount of soil water retained after excess water has drained away.
Field Capacity = Capillary water + Hygroscopic water + Chemically combined water + Water vapor.
The total amount of hygroscopic water and capillary water is the soil's water-holding capacity. The Permanent Wilting Point (PWP) is the level of soil moisture at which plants begin to wilt and cannot recover their firmness. The percentage of soil humidity where a plant first starts to wilt is called the wilting coefficient.
The part of soil water that plants can absorb is called available water, which is usually capillary water. The part that cannot be absorbed is called non-available water. The total amount of soil water is called holard. The portion that can be absorbed is chresard, and the portion that cannot be absorbed is Echard.
Plants need a sufficient amount of water for proper growth. Too much soil water, or waterlogging, reduces the air spaces and damages roots. This affects water absorption and significantly slows plant growth. Land with too much water is called physiologically dry land.
**4. Soil air:**
Soil is porous, with air spaces between soil particles that are filled with either water or air. The amount of soil air depends on the size of these pores. Oxygen in the soil is crucial for seed germination, root growth, soil fertility, humus formation, root hair development, nitrogen fixation by bacteria, and nutrient absorption by roots. Low air circulation can lead to changes in a plant's structure and appearance.
In simple words: Edaphic factors mean how soil affects plants. Soil is formed from rocks, environment, and living things, and it has layers. Good soil has minerals, organic stuff (humus), water, and air. Different types of soil (like sandy or clay) hold water and air differently. Humus is decayed plant and animal matter that makes soil healthy. Soil water from rain is important, but too much or too little is bad. Air in the soil helps roots grow and breathe.

🎯 Exam Tip: For a comprehensive answer on edaphic factors, structure your response to cover soil formation, composition, profile (horizons), and the impact of soil water and air on plant growth and distribution.

Biotic Factors

Answer: Biotic factors refer to all the living activities of organisms, such as growth, getting food, reproduction, and pollination, and how these organisms interact with each other. Odum (1971) divided these interactions into two main groups:
**Positive Interactions:**
In these relationships, one or both species benefit. Examples include mutualism, protocooperation, and commensalism.
1. **Symbiosis:** This is a permanent relationship between two different species where both benefit. It is also known as obligatory mutualism, meaning they often depend on each other for survival. Examples include lichens (a fungus and an alga), Rhizobium bacteria in plant roots, and mycorrhizal associations where fungi connect with plant roots. In such cases, the fungus helps the plant absorb water and minerals (like phosphorus), and in return, the plant provides nutrients to the fungus.
2. **Protocooperation:** This is a temporary relationship between two different species where both benefit, but they don't have to live together to survive (non-obligatory mutualism). For instance, a sea anemone might live on a hermit crab's shell; both benefit, but they can survive independently.
3. **Commensalism:** In this type of relationship, one species benefits, while the other is not affected (it neither gains nor loses).
Examples include:
(i) Epiphytes & Epizoans – Epiphytes are plants that grow on other plants for support, such as Vanda and Orchids. They make their own food and have special hanging roots to absorb moisture from the air. Epizoans are green algae, like Basicladia, that grow on the shells of freshwater animals.
(ii) Lianas – These are long-stemmed woody vines that are rooted in the soil at ground level. They use trees to climb up to the forest canopy to reach well-lit areas. Examples include Tinospora, Bignoia, and Bougainvillea.
**Negative Interactions:**
These are relationships where one or both species are harmed or lose something. This is also called antagonism. There are three types of negative interactions:
1. **Exploitation:** In this relationship, one species directly or indirectly harms another to get support, shelter, or food, mainly for food. Exploitation happens in two forms:

• **Parasitism:** This is a relationship where one organism (the parasite) benefits by living on or in another organism (the host), which is harmed. Examples include leach, dodder (Amarbel), Striga, and Cuscuta.
• **Predation:** This occurs when one animal feeds on other organisms. Herbivores are predators that eat plants, while carnivores are predators that eat other animals. Some fungi (like Dactyella, Zoophagus) and insects are also predators. Certain plants, such as Drosera, Nepenthes, Utricularia, and Dionea, are insectivorous plants that have special organs to trap and feed on insects.

2. **Antibiosis:** In this relationship, one organism releases chemicals that partly or fully stop the growth of another organism, which can lead to its death. For example, the roots of some higher plants secrete toxic chemicals that inhibit the growth of other organisms.
3. **Competition:** This arises when organisms have similar needs and compete for the same limited environmental resources like shelter, food, light, or water. Competition among organisms of the same species is called intraspecific competition, while competition between different species is called interspecific competition.
In simple words: Biotic factors are how living things interact. Some interactions are good, like symbiosis (both benefit, like lichens) or commensalism (one benefits, the other is not affected, like plants growing on trees). Some interactions are bad, like exploitation (one benefits by harming the other, like parasites or predators) or antibiosis (one makes chemicals to stop another from growing) or competition (when living things fight for the same food or space).

🎯 Exam Tip: When discussing biotic interactions, categorize them into positive and negative types. For each type, define it clearly, explain how species interact, and provide specific examples to illustrate the concept effectively.