How do the following organisms act as bio-fertilizers? Explain.
(a) Mycorrhiza
(b) Anabaena
(c) Rhizobium
(a) Mycorrhiza
(b) Anabaena
(c) Rhizobium
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Solution and Explanation
Mycorrhiza: A symbiotic association between fungi and plant roots. Enhances water and nutrient absorption, particularly phosphorus.
Anabaena: A cyanobacterium capable of nitrogen fixation. Provides nitrogen to plants in a usable form and enhances soil fertility.
Rhizobium: A bacterium that forms nodules on the roots of leguminous plants. Converts atmospheric nitrogen into ammonia, which is used by the plant.
Top Questions on Reproduction in Organisms
- Given below is a list of some commercially important products in column A, whereas in column B are names of source organisms:
\[ \begin{array}{|l|l|} \hline \textbf{Column A (Bioactive Products)} & \textbf{Column B (Source Organisms)} \\ \hline A. \text{Cyclosporin – A} & i. \text{Streptococcus} \\ B. \text{Statins} & ii. \text{Trichoderma polysporum} \\ C. \text{Streptokinase} & iii. \text{Penicillium notatum} \\ D. \text{Penicillin} & iv. \text{Monascus purpureus} \\ \hline \end{array} \]
Select the option where the product and their source organisms are correctly matched.
- CBSE CLASS XII - 2024
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- Assertion (A): Some aquatic ecosystems have inverted biomass pyramids.
Reason (R): More energy is required by organisms occupying higher trophic levels.- CBSE CLASS XII - 2024
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- Explain the events that take place once a sperm reaches the oviduct till it becomes a foetus. Write the role of placenta in pregnancy.
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- (A) (i) Name three techniques/devices used by human females to avoid pregnancy. Mention the side effects caused by each.
(ii) What will happen if in a human female (a) fertilisation takes place, (b) an egg is not fertilised?OR
(B) (i) Draw a diagram showing spore formation in Rhizopus and label the (a) reproductive and (b) non-reproductive parts. Why does Rhizopus not multiply on a dry slice of bread?
(ii) Name and explain the process by which reproduction takes place in Hydra.- CBSE Class X - 2024
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- Who proposed that the first form of life could have come from pre-existing non-living organic molecules?
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Questions Asked in CBSE CLASS XII exam
A bacteria sample of a certain number of bacteria is observed to grow exponentially in a given amount of time. Using the exponential growth model, the rate of growth of this sample of bacteria is calculated. The differential equation representing the growth is:
\[ \frac{dP}{dt} = kP, \] where \( P \) is the bacterial population.
Based on this, answer the following:
- CBSE CLASS XII - 2024
- Differentiability
Self-study helps students to build confidence in learning. It boosts the self-esteem of the learners. Recent surveys suggested that close to 50% learners were self-taught using internet resources and upskilled themselves. A student may spend 1 hour to 6 hours in a day upskilling self. The probability distribution of the number of hours spent by a student is given below:
\[ P(X = x) = \begin{cases} kx^2 & {for } x = 1, 2, 3, \\ 2kx & {for } x = 4, 5, 6, \\ 0 & {otherwise}. \end{cases} \]
Based on the above information, answer the following:
- CBSE CLASS XII - 2024
- Probability Distribution
A scholarship is a sum of money provided to a student to help him or her pay for education. Some students are granted scholarships based on their academic achievements, while others are rewarded based on their financial needs.
Every year a school offers scholarships to girl children and meritorious achievers based on certain criteria. In the session 2022–23, the school offered monthly scholarships of ₹3,000 each to some girl students and ₹4,000 each to meritorious achievers in academics as well as sports.
In all, 50 students were given the scholarships, and the monthly expenditure incurred by the school on scholarships was ₹1,80,000.
Based on the above information, answer the following questions:
- Using integration, find the area of the region enclosed between the curve \( y = \sqrt{4 - x^2} \), and the lines \( x = -1 \), \( x = 1 \), and the \( x \)-axis.
- CBSE CLASS XII - 2024
- Integration
- The perimeter of a rectangular metallic sheet is 300 cm. It is rolled along one of its sides to form a cylinder. Find the dimensions of the rectangular sheet so that the volume of the cylinder so formed is maximum.
- CBSE CLASS XII - 2024
- Absolute maxima and Absolute minima