All questions of Organisms and Their Relationships for Grade 9 Exam

The birth rate of a population = new individual added / previous population. Here birth rate= 7/23=0.3043. Hence, birth rate of Salvinia plants is equal to 0.3.###@

Ecology is the branch of biology that studies the relationships between living organisms and their environment. It is concerned with understanding how organisms interact with both the biotic (living) and abiotic (non-living) components of their surroundings.

Logistic growth

Logistic growth is a growth pattern that occurs when resources become progressively limiting in a population. It is a more realistic model of population growth compared to exponential growth, which does not take into account the carrying capacity of an environment.

Understanding logistic growth

Logistic growth is characterized by an initial exponential increase in population size, followed by a slowing down of growth as resources become limited. This is because as a population grows, it will eventually reach a point where there are not enough resources (such as food, water, and shelter) to support further growth.

Factors affecting logistic growth

Several factors influence the occurrence of logistic growth in a population:

1. Carrying capacity: The carrying capacity is the maximum number of individuals that an environment can sustainably support. As a population reaches this limit, resources become increasingly scarce, causing growth to slow down.

2. Density-dependent factors: These are factors that have a greater impact on population growth as population density increases. Examples include competition for resources, predation, and disease. As population density increases due to exponential growth, these factors become more significant in limiting growth.

3. Birth and death rates: In a logistic growth model, birth rates initially exceed death rates, leading to exponential growth. However, as resources become limiting, birth rates start to decline, and death rates may increase due to increased competition and reduced access to resources.

Graphical representation

Logistic growth is often represented graphically using an S-shaped curve. In the initial phase, the curve rises steeply, representing exponential growth. As the population approaches the carrying capacity, the curve levels off and reaches a plateau, indicating the slowing down of growth. At the carrying capacity, the population stabilizes and remains relatively constant.

Significance of logistic growth

Understanding logistic growth is crucial in ecology and population biology. It helps us predict and manage populations, determine the impacts of resource availability on population dynamics, and assess the sustainability of ecosystems. By considering the carrying capacity and the factors that influence population growth, we can make more accurate predictions and develop effective conservation and management strategies.

Logistic growth occurs when populations experience exponential growth under ideal conditions but eventually slow down and level off as resources become limited. The population size stabilizes around the environment's carrying capacity, where growth is regulated by factors like food availability, space, and other ecological constraints.

Mutualism is a type of interaction between two species in which both species benefit from the relationship. This type of interaction is considered to be mutually beneficial and can occur in a variety of ecosystems and between different types of organisms.


Mutualism is a form of symbiotic relationship where both species involved benefit from the interaction. It is a cooperative interaction that enhances the survival, growth, and reproduction of both species.


There are numerous examples of mutualism in nature, demonstrating the wide range of organisms that can engage in this type of interaction. Here are a few examples:

• Pollination: Bees and flowers have a mutualistic relationship. Bees obtain nectar from flowers, which provides them with a food source, while flowers benefit from the transfer of pollen from one flower to another, facilitating reproduction.


• Cleaner Fish and Host Fish: Cleaner fish, such as cleaner wrasses, remove parasites and dead skin from host fish. The cleaner fish benefits by obtaining food, while the host fish benefits from the removal of parasites, improving its health and well-being.


• Leafcutter Ants and Fungus: Leafcutter ants cultivate fungus gardens by cutting and transporting leaves. The ants feed on the fungus, while the fungus benefits from the constant supply of organic matter and protection provided by the ants.

Mutualism is advantageous for both species involved due to the following reasons:

1. Resource Sharing: Both species share resources, such as food, shelter, or protection, which increases their chances of survival and reproduction.


2. Increased Fitness: By working together, both species can increase their overall fitness and reproductive success. This can lead to population growth and long-term survival.


3. Enhanced Nutrient Cycling: Mutualistic relationships can improve nutrient cycling in ecosystems, benefiting the overall health and productivity of the environment.

Mutualism is a type of interaction that benefits both species involved. It is a cooperative relationship that enhances survival, growth, and reproduction. Examples of mutualism can be found in various ecosystems, demonstrating the importance of this type of interaction in nature.

Explanation:

Introduction:
Xerophytes are plants that have adapted to survive in dry and arid conditions. They have evolved various characteristics to minimize water loss and maximize water uptake. Some of these adaptations include reduced leaves, sunken stomata, and the ability to perform CAM (Crassulacean Acid Metabolism). However, one characteristic that should not be present in any xerophyte is the absence of the cuticle.

Explanation:

The cuticle:
The cuticle is a waxy layer that covers the surface of leaves and stems. It acts as a barrier to prevent water loss by reducing transpiration. The cuticle is made up of a lipid layer called cutin, which is impermeable to water. This helps to retain water within the plant and protect it from desiccation.

Importance of the cuticle:
The cuticle plays a vital role in the survival of plants in dry environments. It reduces the rate of water loss through transpiration by acting as a physical barrier. In xerophytes, the cuticle is often thicker and more pronounced than in mesophytes (plants adapted to moderate moisture conditions). This helps to prevent excessive water loss in xerophytes, allowing them to survive in arid environments.

Why absence of cuticle should not be a characteristic feature of xerophytes:
The absence of the cuticle in xerophytes would result in increased transpiration and water loss. This would be detrimental to the survival of xerophytes in dry conditions, as it would lead to rapid dehydration and desiccation. The cuticle acts as a protective layer, reducing water loss and helping xerophytes to conserve water. Therefore, the absence of the cuticle would be counterproductive and not a characteristic feature of xerophytes.

Conclusion:
In summary, xerophytes are plants that have adapted to survive in dry environments. They possess various adaptations to minimize water loss and maximize water uptake. While characteristics such as reduced leaves, sunken stomata, and CAM are common in xerophytes, the absence of the cuticle should not be a characteristic feature. The cuticle plays a crucial role in reducing water loss through transpiration and helps xerophytes to conserve water in arid conditions.