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Cell : The Unit of Life

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Biology

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Biology

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Class 10 Class 12

How do neutral solutes move across the plasmalemma ? Can the polar molecules also move across it in the same way ? If not, then how are these transported across the membrane? 


The neutral solutes move across the plasma membrane by simple diffusion. They diffuse across the membrane along their concentration gradient that is from their higher concentration to their lower concentration.

Passage of polar molecules : Due to bilayer of nonpolar lipid molecules, the polar molecules cannot pass through biomembranes. They require carrier molecules to facilitate their transportation across membrane. The transport of certain molecules takes place against their concentraion gradient from lower to higher concentration, this process requires energy and is an active transport process. The energy is provided by ATP.

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Name two cell-organelles that are double membrane bound. What are the characteristics of these two organelles ? State their function and draw labelled diagrams of both.

 Chloroplasts and mitochondria are organelles which have double membrane . 

Mitochondria - is called the power house of the cell as it produces cellular energy in the form of ATP. It is bounded by two membrane, the inner membrane forms inner foldings called cristae. The matrix has a single circular DNA molecule. 

Chloroplasts - are also double membrane bound organelles which help to trap the solar energy and produce food. The stroma contains many flattened disc like structures called thylakoids which are arranged in stacks to gorm grana. The chloroplasts consists of the pigment chlorophyll that helps to convert sun's energy to chemical energy. 

Functions of :

Mitochondria - It produces the cellular energy in the form of ATP.

Chloroplasts - trap the energy of the sun and produce food.





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What are the characteristics of prokaryotic cells?

Characteristics of Prokaryotic cell are as follows:

1. The nucleus is not bounded by a membrane.

2. Their genetic material is naked and present in the form of nucleoid in the cytoplasm.

3. They are generally smaller and divide more rapidly as compared to the eukaryotic cell.

4. They are usually surrounded by cell wall except for mycoplasma.

5. Besides genomic DNA many prokaryotic cell have small circular DNA called plasmids outside the genomic DNA.

6. Eukaryotic organelles or membrane bound organelles are not found in the prokaryotic cells. The ribosomes found in these are of 70S type. 

7. Mesosomes which are the invaginations of plasma membrane may be present.

8. They have special inclusion bodies. 

 

 

 

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What is a centromere ? How does the position of centromere form the basis of classification of chromosomes. Support your answer with a diagram showing the position of centromere on different types of chromosomes.

Centromere is a primary constriction present in the chromosome. It provides orientation to chromosome and marks the space for attachment of chromosomal fibres during cell division. The centromere has disc shaped structures called kinetochores on the sides of it.

Depending upon the location of centromere in a chromosome, the chromosome is classified  into the following four types :

(a) Telocentric: Centromere is present at the terminals.

(b) Acrocentric: Centromere is present near the terminals resulting in two short arms and two long arms. 

(c) Sub- metacentric : Centromere divides the chromosomes into two unequal arms. It lies either below centre or above centre.

(d) Metacentric : Centromere divides the chromosomes into two equal arms with the centromere in the middle.

 

 

What is a centromere ? How does the position of centromere form the basis of classification of chromosomes. Support your answer with a diagram showing the position of centromere on different types of chromosomes.

 

What is a centromere ? How does the position of centromere form the basis of classification of chromosomes. Support your answer with a diagram showing the position of centromere on different types of chromosomes.

 

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What are nuclear pores ? State their function.

Nuclear pores are pores in nuclear membrane. They are are formed by the fusion of its two membranes.

Functions of nuclear pores :

1. The materials are exchanged between cytoplasm and nucleus through nuclear pores.

2. The proteins are passed in and out of the nucleus through nuclear pores.

3. The enzymes for synthesis of DNA and RNA are passed into nucleus through nuclear pores.

4. Ribosomal subunits  and RNA are passed out from nucleus via nuclear pores.

5. m RNA and t RNA are passed out into cytoplasm via nuclear pores.

 

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