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+ 3.4%

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Study the graph given below and answer the questions that follow:i Write the status of food and space in the curves a and b ii In the absence of predators, which one of the two curves would appropriately depict the prey population?iii Time has been shown on X-axis and there is a parallel dotted line above it Give the significance of this dotted line. from Biology Organisms and Populations Class 12 Nagaland Board

​Developmental plasticity is a general term referring to changes in neural connections during development as a result of environmental interactions as well as neural changes induced by learning. • The living differentiated cells, that by now have lost the capacity to divide can regain the capacity of division under certain condition is dedifferentiation. Thus, rate of growth can be expressed mathematically. To determine the generation time of given bacteria. To plot standard growth curve of Staphylococcus aureus.

  • One petal resembles the female of a bee species in size, colour, markings, etc.
  • The depletion of nutrients and the subsequent accumulation of metabolic waste products and other toxic materials in the media will facilitates the bacterium to move on to the Death phase.
  • Plotting the body weight of an animal on the ‘y’ axis and the age of the animal on the ‘x’ axis produces growth curve.
  • For example, when the prickly pear cactus was introduced in Australia in early 1920, they spread rapidly causing havoc.Their population was controlled by introducing cactus-feeding predator .

C) The bacteria do not multiply in this phase but prepare the necessary and essential factors, ribosomes, proteins and enzymes that are required for conducting important physiological and molecular processes. Iii) The stationary phase is the phase of retardation of growth. Elongation phase is the one in which the cells elongate by changing their size of vacuoles, the mass of protoplasm, etc.

3 Sterilisation Time

Thermo word derived from Greek word ” thermolita ” meaning heat and philia meaning love . Head loving microorganisms mostly growth in 45 ℃ to 80 ℃ temperature . In this phase bacterial size increase but not increase number of cell.

The overkill method is used when the product can withstand excessive heat treatment such as an Fo≥ 12 without adverse effects. Bioburden and resistance data are not required to determine the required ‘Fo’ values. Micro-organisms are killed faster at high temperature than at low temperature. In order to quantify the change in resistance of a micro-organism in response to a change in temperature, the Z-value has been introduced. The Z-value is the number of degrees of temperature increase required to decrease the D-value by a factor 10. SAL also describes the killing efficacy of a sterilisation process.

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The phases of growth in plants are divided into three phases. These are the meristematic phase or phase of cell division, elongation phase or phase of cell elongation and maturation phase or phase of differentiation. The plants show arithmetic and geometric growth rate. The sigmoid curve represents the integrated sum of the curves for each growing organ and cell and presents the changing size of these parts. These are the lag phase, log phase or acceleration phase, stationary phase and death phase.

  • Logistic growth occurs when the population is restricted by some limiting factor.
  • In actual growth curve, the live weight is plotted against age and it has the typical ‘sigmoid’ shape.
  • 44.Explain death rate in a population by taking a suitable example.
  • IndiaBIX provides you lots of fully solved Microbiology questions and answers with Explanation.

Growth whose rate becomes ever more rapid in proportion to the growing total number or size. Population growth can be described with two models based on the size of the population and necessary resources. These two types of growth are known as exponential growth and logistic growth. The bacterial growth curve shows the preparation, division, growth and death of the bacterial cells. The steam condenses on the cold surface, thereby transferring heat to the medical device, which results in heating up to the sterilisation temperature.

Organisms and Populations Important Questions for CBSE Class 12 Biology Population

Lichens represent an intimate mutualistic relationship between a fungus and photosynthesising algae or cyanobacteria. Here, the fungus helps in the absorption of nutrients and provides protection, while algae prepare the https://1investing.in/ food. Commensalism is the interaction between two species, where one species is benefitted and the other is neither harmed nor-benefitted. Human liver fluke depends on two intermediate hosts to complete its life cycle.

Amensalism This is an interaction, where one species is harmed, while other neither benefitted nor harmed, e.g. antibiotics for pathogens. Extinction of bumble bee will definitely affect the orchid flower because these bees are the means of pollination for the flower and if they get extinct, the pollination percentage will be reduced. But, the extinction of the orchid will not affect the bumble bee population.

What type of growth model represents human population growth to the present?

An overall increase occurs in plant growth and development. Through reproduction, 10 new Hydrilla plants were added in a year. Ecologists suggest that life history traits of organisms have evolved in relation to the constraints imposed by the abiotic and biotic components list down the disadvantages of unemployment of the habitat in which they live. Logistic growth occurs when resources become limited at certain point of time, so no population can grow exponentially. Positive acceleration phase- Limited growth in population is seen as the resources become available.

types of curves are obtained in the growth of organism

When a bacterial population is inoculated into new fresh media the cells do not reproduce immediately in a new medium. During the lag phase, bacteria take some time adapt themselves to the new growth conditions. When microorganisms are grown in a suitable liquid medium and incubated its growth follows a definite process. If bacterial counts are carried out at intervals after inoculation and plotted in relation to time, a growth curve is obtained. Therefore, it is essential to reduce the initial contamination as much as possible before sterilisation. However this time period may be somewhat longer in special cases, according to a risk assessment.

The rate of growth of the bacterial cells is limited by the accumulation of toxic compounds and also depletion of nutrients in the media. The cell population remains constant at this stage. Plotting this phase on the graph gives a smooth horizontal linear line.

Which organisms are greater in number autotrophic or heterotrophic Why?

Autotrophs are the organisms which are greater in number. It is because heterotrophs are dependant on autotrophs to meet their food requirements. If heterotrophs exceed the number of autotrophs, then all the autotrophs will vanish and so will be the heterotrophs.

Mention the essential information that can be obtained by studying the population density of an organism. List any three ways of measuring population density of a habitat. Ans.A-Exponential growth curve When the resources are not limiting, this form of curve appears. Whereas mutualism is the type of interaction in which both the species involved are benefitted. Ans.The interaction between a clown fish living among the tentacles of sea anemone is called commensalism.

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This phase is situated just next to the meristematic zone, away from the growing tip. The steam steriliser is commonly referred to as an autoclave. The simplest steam steriliser, however, is a pressure cooker. In a pressure cooker, the added distilled or deionised water is heated and eventually begins to boil.

17.List two advantages that a mycorrhizal association provides tO the plant. Ans.Camouflage is a prey defence mechanism to avoid being detected easily by the predators. Ans.Phytophagous insects feed on sap and other parts of plants.

Why are consumers dependent on producers cite an example?

Consumers have to feed on producers or other consumers to survive. Deer are herbivores, which means that they only eat plants (Producers). Bears are another example of consumers. Black bears are omnivores and scavengers, like skunks and raccoons, which means that they will eat just about anything.