Mitosis: Cell Division Explained

Producing New Cells

• Body cells, excluding sperm and egg cells, are diploid, containing two matching sets of chromosomes.
• One chromosome set comes from the mother, and the other is from the father.
• Cell division is necessary for growth, repairing damaged tissues, and replacing old or dead cells.
• Mitosis divides cells in several steps:

Steps of Mitosis

• Chromosomes shorten and thicken, becoming visible under a microscope. Each chromosome appears as an 'X' shape, composed of two chromatids.
• Chromosomes align along the cell's equator. Spindle fibers, which are rope-like structures, attach to the middle of each chromosome.
• Spindle fibers pull chromatids apart toward opposite poles of the cell. Separated chromatids are then referred to as chromosomes.
• The nuclear membrane reforms, resulting in a single cell with two nuclei for a short time.
• The cytoplasm divides, leading to the formation of two new, identical daughter cells that are diploid and have the same DNA as the original cell.

Stem Cells

• Stem cells are unspecialized cells crucial for growth and repair, with two key abilities:
• Self-renewal: the capacity to create more stem cells.
• Specialization: the ability to transform into specific cell types to replace or renew existing specialized cells.
• There are two types of stem cells:
  • Embryonic Stem Cells: These are located only in embryos and have the ability to differentiate into any type of human cell.
  • Tissue Stem Cells: These are located only in adults and can only differentiate into a few different cell types

Organisation of the Human Body

• The human body is multicellular, meaning it is made of more than one cell, unlike unicellular organisms like bacteria.
• Similar cells form tissues, tissues combine to create organs, and organs work together in systems.
• This hierarchical organization ranges from specialized cells to tissues, organs, and systems, eventually forming a complete organism.

Control and Communication - Nervous System

• The central nervous system (CNS), including the brain and spinal cord, and nerves make up the nervous system.
• The brain consists of the cerebrum which controls personality and memory; the cerebellum which controls balance and coordination; and the medulla which controls for breathing and heart rate.
• Sensory neurons carry electrical impulses from receptors to the CNS. Interneurons, found within the CNS, process sensory information. Motor neurons transmit electrical impulses from the CNS to effectors, enabling responses.
• Receptors change a stimulus into an electrical signal, while effectors, such as muscles or glands, generate a response.
• Synapses are gaps between neurons where chemical signals transfer the nerve impulse.
• A reflex arc is a special nerve pathway for quick, automatic responses that bypasses the brain to protect the body from injury.

Control and Communication - Hormonal System

• Endocrine glands produce hormones, which are chemical messengers made from protein and travel in the bloodstream to target tissues.
• Target tissues have cells with specific receptor proteins that match certain hormones, ensuring that only these tissues are affected.
• Blood glucose levels are regulated by insulin and glucagon.
  • Insulin lowers blood glucose by converting glucose to glycogen in the liver. Glucagon increases blood glucose by converting glycogen back into glucose in the liver.

Reproduction

• Sexual reproduction in plants and animals requires gametes, specialized haploid cells (containing one set of chromosomes).

Gametes in Animals:

 - Male sex cells (sperm) are produced in the testes.
 - Female sex cells (egg) are produced in the ovaries.

Gametes in Plants:

 - Male sex cells (pollen) are produced in the anthers.
 - Female sex cells (ova) are produced in the ovary.

• Fertilization is the fusion of two haploid gamete nuclei to produce a diploid zygote. That zygote then divides to form an embryo.

Variation and Inheritance

• Variation results from differences within a species.
• Discrete Variation: Measurements fall into distinct groups
• Continuous Variation: There is a range of measurements between a maximum and minimum.
• Single gene inheritance results in discrete variation. Polygenic inheritance results in continuous variation.
• Genes are short DNA strands coding for proteins, with alleles as different versions of the same gene.
• Phenotype is the physical description determined by the genotype which is the allele description.
• Dominant alleles determine the phenotype, while recessive alleles can be masked by dominant ones.
• Homozygous genotypes have identical alleles and heterozygous genotypes have different alleles.
• The parental generation is P1, the first offspring generation is F1, and the second offspring generation is F2.
• A monohybrid cross predicts offspring from two parents, using a Punnett square.

Transport Systems - Plants

• Xylem transports water, while phloem transports sugar.
• Xylem is composed of dead tissue with lignified cells for strength, transporting water and minerals upwards only. Phloem is living tissue with sieve plates and companion cells, transporting sugar both upwards and downwards.
• Transpiration is how water moves from the roots to the leaves.
  • Water enters the roots through osmosis, travels up the stem in the xylem, moves into the leaf through veins, and evaporates through the stomata.

Factors Affecting Transpiration Rate:

 - Wind Speed: Higher speeds increase transpiration.
 - Temperature: Higher temperatures increase transpiration.
 - Surface Area: Larger leaf surface areas increase transpiration.
 - Humidity: Higher humidity decreases transpiration.

• Leaves have four tissue layers. Their veins contain xylem and phloem. Stomata on the leaf underside, controlled by guard cells, regulate water loss.

Transport Systems - Animals

• Arteries carry blood away from the heart, have thick, muscular walls and narrow channels, and operate under high pressure.
• Veins carry blood to the heart, have thinner walls and wider channels, operate under lower pressure, and contain valves to prevent backflow.
• Capillaries facilitate material exchange with very thin walls and a large surface area.
• The right side of the heart pumps deoxygenated blood to the lungs. The left side pumps oxygenated blood to the body.
• The heart has four chambers (two atria, two ventricles) and four valves to ensure correct blood flow direction.
• Arteries supplying the heart muscle are coronary arteries.

  Components of blood:

  • Red blood cells carry oxygen using hemoglobin.
  • White blood cells destroy pathogens, including phagocytes that engulf pathogens.
  • Lymphocytes produce antibodies.

Absorption of Materials

• Materials that need to be absorbed into the bloodstream are the oxygen and nutrients (delivered to cells) and removal waste in carbon dioxide (removed from cells)
• Capillary networks are need to allow for this exchange
• Features that increase the efficiency of absorbtion are a good blood supply, larger surface and thin walls

Small Intestine

• The small intestine absorbs food nutrients. Its walls contain thousands of villi, increasing the surface area. Each villus has a capillary network for glucose and amino acid absorption, and a lacteal for fatty acid and glycerol absorption.

Gas Exchange in Lungs:

• The lungs have many alveoli for gas exchange. Oxygen crosses the thin alveolar walls into the bloodstream. Carbon dioxide leaves the capillaries and crosses into the alveoli to be exhaled.