Cells and control Revision Notes

Animal Growth: Cell Division and Differentiation

Animal growth primarily involves cell division (mitosis) to increase the number of cells. These new cells then undergo differentiation, where they become specialised for specific functions, forming tissues and organs. Most animal growth occurs during development and childhood, with some cell replacement and repair continuing in adulthood. Stem cells play a crucial role in providing new cells for growth and repair.

Plant Growth: Division, Elongation, and Differentiation

Plant growth is localised to meristems. It involves three key stages: 1) Cell division (mitosis) to produce new cells, primarily at meristems. 2) Cell elongation, where new cells absorb water and expand, significantly increasing their size. This elongation is a major contributor to plant growth. 3) Differentiation, where elongated cells develop specialised structures and functions to form various plant tissues, such as root hair cells, palisade cells, and guard cells.

The Role of Differentiation

Differentiation is the process by which a less specialised cell becomes a more specialised cell type. This specialisation allows cells to perform specific functions, contributing to the overall efficiency and complexity of the organism. In both plants and animals, this process is essential for forming the diverse tissues and organs necessary for life.

Purpose of Mitosis

Mitosis is a type of cell division that produces two daughter cells from a single parent cell. Its primary role is in growth, general cell replacement, and repair of tissues. For example, when you cut yourself, new skin cells are produced by mitosis to heal the wound.

Process and Outcome

Before mitosis, the cell duplicates its chromosomes. Each chromosome then consists of two identical copies. During mitosis, these copies separate, ensuring each new cell receives a full and identical set of chromosomes. The result is two genetically identical diploid body cells, meaning they have the same genetic information and number of chromosome sets (two) as the original parent cell.

Components of the Nervous System for Impulse Transmission

Sensory receptors detect stimuli and generate electrical impulses. Sensory neurones transmit these impulses from receptors to the central nervous system (CNS). Relay neurones, found in the CNS, link sensory and motor neurones, or other relay neurones. Motor neurones transmit impulses from the CNS to effectors (muscles or glands), causing a response. The axon is a long fibre that carries impulses away from the cell body. The dendron is a long fibre that carries impulses to the cell body (found in sensory neurones). Cell bodies contain the nucleus and most cellular organelles.

Synaptic Transmission and Myelin Sheath

Synapses are junctions where electrical impulses are transferred between neurones using chemical neurotransmitters. When an impulse reaches the presynaptic terminal, neurotransmitters are released into the synaptic cleft. These diffuse across the cleft and bind to receptors on the postsynaptic membrane, generating a new impulse or response. Neurotransmitters are chemical messengers that enable signals to cross the synaptic gap. The myelin sheath is a fatty layer around axons and dendrons that insulates them and increases the speed of electrical impulse conduction.

What is Cell Differentiation?

Cell differentiation is the process where a general, unspecialised cell changes into a specific, specialised cell type. This is essential for forming the many different cell types found in multicellular organisms, each with unique structures and functions.

Importance of Specialised Cells

Specialised cells are vital because they allow different parts of an organism to perform specific jobs efficiently. For instance, red blood cells are specialised to carry oxygen, nerve cells to transmit signals, and muscle cells to contract. This division of labor improves overall organism function.

Developmental Process

All specialised cells in a multicellular organism originate from a single fertilised egg (zygote). Through repeated cell division and differentiation, the zygote develops into an embryo, and then a foetus, with cells taking on specific roles to form tissues, organs, and organ systems.