Latest questions in this category.
A centrosome usually contains two perpendicular cylindrical centrioles surrounded by amorphous pericentriolar material. Each centriole possesses a cartwheel-like organisation formed from peripheral triplets and radial spokes.
Ref: NCERT Class 11 Biology Chapter 8: Cell: The Unit of Life Cytoskeleton Cilia Flagella Centrosome Nucleus and Chromosomes
Interphase chromatin is loose and indistinct, whereas structured chromosomes become visible during cell division. A centromere slightly away from the middle produces one shorter and one longer arm, identifying a submetacentric chromosome.
Ref: NCERT Class 11 Biology Chapter 8: Cell: The Unit of Life Cytoskeleton Cilia Flagella Centrosome Nucleus and Chromosomes
The axoneme of a eukaryotic cilium or flagellum usually has a 9+2 arrangement of peripheral doublets and central microtubules. A centriole has nine peripheral triplets connected to a proteinaceous hub by radial spokes.
Ref: NCERT Class 11 Biology Chapter 8: Cell: The Unit of Life Cytoskeleton Cilia Flagella Centrosome Nucleus and Chromosomes
A metacentric chromosome has a centrally positioned centromere and two equal arms. A telocentric chromosome has a terminal centromere. Classification therefore requires relating arm lengths to centromere position.
Ref: NCERT Class 11 Biology Chapter 8: Cell: The Unit of Life Cytoskeleton Cilia Flagella Centrosome Nucleus and Chromosomes
A membrane-covered structure with a 9+2 axoneme is a eukaryotic cilium or flagellum. Bacterial flagella are structurally different, while centrioles possess nine peripheral triplets rather than a 9+2 arrangement.
Ref: NCERT Class 11 Biology Chapter 8: Cell: The Unit of Life Cytoskeleton Cilia Flagella Centrosome Nucleus and Chromosomes
Centrioles form the basal bodies of cilia and flagella. In animal cells, they also form spindle fibres that give rise to the spindle apparatus during cell division.
Ref: NCERT Class 11 Biology Chapter 8: Cell: The Unit of Life Cytoskeleton Cilia Flagella Centrosome Nucleus and Chromosomes
A prokaryotic cell lacks a well-defined nucleus. Its genomic DNA is generally a single circular chromosome that remains naked because it is not enclosed by a nuclear membrane. Plasmids, when present, occur in addition to the genomic DNA.
Ref: NCERT Class 11 Biology Chapter 8: Cell: The Unit of Life Cytoskeleton Cilia Flagella Centrosome Nucleus and Chromosomes
Unicellular organisms demonstrate that a complete cell can exist independently and perform essential life functions. A structure smaller than a complete cell does not ensure independent living.
Ref: NCERT Class 11 Biology Chapter 8: Cell: The Unit of Life Cytoskeleton Cilia Flagella Centrosome Nucleus and Chromosomes
The number of mitochondria varies among cells according to their physiological activity. Mitochondria also show considerable variation in shape and size.
Ref: NCERT Class 11 Biology Chapter 8: Cell: The Unit of Life Cytoskeleton Cilia Flagella Centrosome Nucleus and Chromosomes
A centriole has nine evenly spaced peripheral fibrils, each composed of a microtubule triplet. A proteinaceous central hub is connected to the peripheral triplets by radial spokes.
Ref: NCERT Class 11 Biology Chapter 8: Cell: The Unit of Life Cytoskeleton Cilia Flagella Centrosome Nucleus and Chromosomes
The centromere is the primary constriction of a chromosome and holds its two chromatids together. Disc-shaped structures called kinetochores are present on the sides of the centromere.
Ref: NCERT Class 11 Biology Chapter 8: Cell: The Unit of Life Cytoskeleton Cilia Flagella Centrosome Nucleus and Chromosomes
The nuclear envelope consists of two parallel membranes separated by a space of approximately 10–50 nm. This intervening region is called the perinuclear space.
Ref: NCERT Class 11 Biology Chapter 8: Cell: The Unit of Life Cytoskeleton Cilia Flagella Centrosome Nucleus and Chromosomes
