Cells and control revision notes

Purpose of Mitosis

Mitosis is the process of cell division that produces two, genetically identical diploid daughter cells. This is essential for organismal growth, repair of damaged tissues, and asexual reproduction. It ensures that new cells have the same genetic information as the parent cell.

Process of Mitosis

Before mitosis, the cell's chromosomes are replicated. During mitosis, these replicated chromosomes (each consisting of two sister chromatids) align, and the sister chromatids are then separated, moving to opposite ends of the cell. Finally, the cell divides, forming two new daughter cells. Each daughter cell receives a full and identical set of chromosomes to the parent cell's nucleus, maintaining the diploid number.

Genetic Outcome

The outcome of mitosis is the formation of two daughter cells that are genetically identical to each other and to the original parent cell. These cells are diploid, meaning they contain two complete sets of chromosomes. This genetic fidelity is vital for maintaining the integrity of an organism's genetic material across cell generations for bodily functions like tissue regeneration.

Neurone Types and Their Functions

There are three main types of neurones involved in reflex arcs and nervous responses: sensory neurones, relay neurones, and motor neurones. Sensory neurones transmit impulses from receptors to the central nervous system (CNS). Relay neurones are found within the CNS and connect sensory neurones to motor neurones, allowing for processing. Motor neurones transmit impulses from the CNS to effectors (muscles or glands) to produce a response.

Neurone Structure and Myelin

Neurones consist of a cell body, dendrons, and an axon. Dendrons are short, branched extensions that receive impulses. The axon is a long extension that transmits impulses away from the cell body. Many axons are covered by a myelin sheath, an insulating layer that increases the speed of impulse transmission. Without myelin, impulses would travel much slower, impacting reaction times significantly.

Synaptic Transmission

Synapses are junctions where impulses are transmitted between neurones, or between a neurone and an effector. Electrical impulses cannot cross the synaptic gap (cleft). Instead, neurotransmitters are released from the pre-synaptic neurone into the cleft. These chemicals diffuse across and bind to receptors on the post-synaptic membrane, initiating a new impulse or stimulating a response. This ensures one-way flow of information.

What is a Reflex Arc?

A reflex arc is the neural pathway that controls a reflex action. It is an involuntary, rapid response to a stimulus, primarily serving a protective function. This pathway bypasses the brain for conscious decision-making, allowing for faster reactions.

Components of a Reflex Arc

The reflex arc consists of three key types of neurons: sensory, relay, and motor neurons. Sensory neurons detect stimuli and transmit impulses to the CNS. Relay neurons, found within the CNS (spinal cord), connect sensory and motor neurons. Motor neurons transmit impulses from the CNS to effector organs, such as muscles or glands, which then carry out the response.

Pathway of a Reflex Impulse

1. Stimulus Detection: A sensory receptor detects a stimulus.
2. Sensory Neuron: Transmits the nerve impulse from the receptor to the spinal cord.
3. Relay Neuron: In the spinal cord, it receives the impulse from the sensory neuron and passes it to a motor neuron.
4. Motor Neuron: Carries the impulse from the spinal cord to an effector (e.g., muscle).
5. Effector Response: The effector carries out the appropriate action (e.g., muscle contracts).

Embryonic Stem Cell Function

Embryonic stem cells are found in very early animal embryos. They are pluripotent, which means they can differentiate into almost every cell type in the body. Their primary function is to form all the tissues and organs during embryonic development, leading to the formation of a complete multi-cellular organism.

Adult Animal Stem Cell Function

Adult stem cells are found in some tissues and organs throughout an animal's life. They are multipotent, meaning they can differentiate into a limited range of cell types within specific tissues. Their main function is to replace dead or damaged cells, facilitating tissue repair and maintenance, such as blood cells from bone marrow stem cells.

Meristem Function in Plants

Meristems are regions in plants containing meristematic cells, which are plant stem cells. These cells are totipotent, meaning they can differentiate into any plant cell type. Meristems are responsible for the plant's continuous growth, forming new stems, roots, leaves, and flowers throughout its lifespan. Examples include apical meristems at shoot and root tips, and lateral meristems for girth.