Biology 12 Organism and Populations Chapter 13 – Exercise,
Diapause. It is the phenomenon of spending unfavorable climatic conditions by insects during their development.
- Growth forms
- Population density
- Population dispersion
- Population age distribution
Ans 6. 1. Modification of leaves into thorns.
- Development of spiny margins on leaves.
- Development of sharp silicate edges in leaves.
Q 9. Distinguish between the following.
- Hibernation and aestivation
- Ectotherms and endotherms.
Ans 9. a. the phenomenon of spending old period in an inactive stage by an animal is called hibernation. On the other hand, the phenomenon of spending dry-hot period in an inactive stage is called aestivation.
- ectotherms are the cold-blooded animals having body temperature matching with the environmental temperature. They are affected by temperature variations.
Endotherms are warm-blooded animals who can regulate their body temperature y physiological means and maintain more of less constant internal temperature.
Q 10. Write a short note on:
- Adaptations of desert plants and animals.
- Adaptations of plants to water scarcity.
- Behavioral adaptations in animals.
- Importance of light to animals.
- Effect of temperature on adaptation of animals.
- The most significant adaptation of aquatic plants (hydrophytes) is the presence of aerenchyma with large, air-filled spaces, the lacunae. The aerenchyma stores CO2 and o2 produced in respiration and photosynthesis for reuse in these metabolic processes. The aerenchyma also helps in floating. The most prominent adaptation of the aquatic animals is the arrangement to get oxygen from water. They take up oxygen through the body surface or by way of gills.
Lack and shortage of water kill the aquatic plants. Fish and many invertebrates die when streams, tanks and ponds dry up in summer. During periods of law water level, the water temperature may rise sufficiently to kill the inhabitants. Some aquatic animals manage to survive the drought periods by forming thick walled cysts or by laying heavy-shelled eggs or by undergoing aestivation.
- Many species of plants are adapted to dry habitats and high temperature conditions e.g. plants of hot deserts. They are termed as xerophytes. The xerophytes have special adaptations to withstand prolonged period of drought. These are of four types-
Ephemerals (drought escapers),
Annuals (drought evaders),
Succulents (drought resistant) and
Non-succulent perennials (drought endures).
- Living organisms, over a period of time, have adapted themselves to changes in the external environment in different ways. Some organisms (e.g., birds mammals) have evolved to maintain a constant body temperature even under changed environmental conditions. They maintain homeostasis (Gk. Homois = alike, stasis = position) through physiological means by spending a lot of energy of the body. However, a large number of organisms are not able to spend so much or energy for maintaining homeostasis.
- Sunlight is the source of energy for practically all organisms: plants, animals and microbes. Green plants trap sunlight to manufacture food by photosynthesis. The energy stored in the organic compounds produced by plants is used is used partly by themselves and partly by all animals directly or indirectly. The microorganisms get energy by decomposing the dead organic matter.
During the daylight of determines the time of flowering in plants and growth in trees. According to their response to the length of daylight. The plants are of 3 types.
1 – Long-day plants
2 – Short-day plants
3 – Day-neutral plants
- The animals with variable temperature, called poikilotherms, are affected by temperature variations more than the homeotherms. They are also called ectotherms (cold-blooded animals; their body temperature tends to match with the environmental temperature in which they live. Nearly 99% of animals and almost all plants belong to this category. Such organisms where body temperature and body fluid osmolality change with that of the ambient environment are called conformers. They fight temperature variation in the following manner: Hibernation, Aestivation, Periodic Activity, winter eggs and migration.
Q 12. Give an example for:
- An endothermic animal
- An ectothermic animal
- An organism of benthic zone.
- Human being
- Bacteria (decomposers)
Ans 13. A group of individuals of the same species, who interbreed to produce fertile young, living together in the same geographical area at a time is called population.
Community refers to groups of organisms belonging to several different species that live together in the same area of habitat and interact through trophic and spatial relationship.
Q 14. Define the following terms and give one example for each:
- Interspecific competition
- Commensalism is an interspecific interaction between individuals of two species where one species is benefited and other is not affected, e.g., orchid and mango tree.
- Parasitism is an interspecific interaction between individuals of two species where generally small species is benefitted (parasite) and the large species (host) is affected, e.g., malarial parasite and human beings.
- It is the ability of the animals to blend with the surroundings or background. In this way, animals are benefited in an protections or aggression. Example is stick insect.
- Mutualism is an interspecific interaction between individuals of two species both the interacting species are benefitted in an obligatory way. Example. pollination in plants by animals.
- Interspecific competition. It is an interaction between individuals of two species where both the interacting species are affected, e.g, Monarch butterfly and Queen Monarch.
Q 16. Select the statement which explains best parasitism.
- One organism is benefited.
- Both the organisms are benefited.
- One organism is benefited, other is not affected.
- One organism is benefited, other is affected.
Ans 17. The three important characteristics of a population are
- Natality is the rate of production of new individuals per unit population per unit time through birth. It is also called as birth rate and can be calculated as a number of births in a year per thousand individuals. The higher the natality more is the increase in the population.
Natality = Total number of individuals in a Population Number of birth×1000
- Mortality is the loss of new individuals per unit population per unit time through death. It is also called as death rate and can be calculated as a number of deaths in a year per thousand individuals. The higher the mortality more is the decrease in the population.
Mortality = Total number of individuals in a population Number of death × 1000
- Age distribution is the numbers of individuals in various age categories in a given population. It includes the number of people in the pre-reproductive, reproductive and post- reproductive group.
These are the key factors in determining whether a population is increasing, decreasing or stable.