Notes, abstracts, papers, exams and problems of Biology

Wood Structure and Properties

Sapwood and Heartwood

Sapwood

• Width varies with species, growth rate, and tree age.
• Typically represents 20-50% of the total radius (except in very young trees).

Heartwood

• Formed from former sapwood cells.
• Acidity increases, extractives form, and color changes.
• Resistance to fungal and insect attack increases.
• Many timbers develop gums and resins in the heartwood.

Functions of Cells in a Growing Tree

• Primary function: Conduction of water and dissolved minerals from roots to leaves.
• Secondary function: Mechanical support of the tree.
• Tertiary function: Food storage for spring growth.

Characteristic Differences between Softwoods and Hardwoods

• Hardwoods: Water-conducting elements distributed throughout the annual ring.
• Softwoods:

Components of the Circulatory System

The circulatory system consists of various components that work together to transport blood throughout the body. These components include:

Blood

• Plasma: a liquid substance that carries nutrients and waste throughout the body.
• Red blood cells: responsible for carrying oxygen and giving blood its red color.
• White blood cells: protect the body from germs and diseases.
• Platelets: help stop bleeding from wounds.

Blood Vessels

• Arteries: carry blood from the heart to the capillaries.
• Veins: carry blood from the capillaries back to the heart.
• Capillaries: enter body cells to deliver nutrients and oxygen, and remove carbon dioxide and waste.

Heart

The heart is a muscular organ that pumps blood throughout the body via the blood... Continue reading "Components of the Circulatory System: Blood, Blood Vessels, and Heart" »

1. The sound waves travel to the ear canal. This is a tube-shaped opening in the ear.
2. At the end of the ear canal, the sound waves hit the eardrum. This is a thin membrane that vibrates like the head of a drum when sound waves hit it.
3. The vibrations pass from the eardrum to the hammer. This is the first of three tiny bones that pass vibrations through the ear.
4. The hammer passes the vibrations to the anvil, the second tiny bone that passes vibrations through the ear
   
5. The anvil passes the vibrations to the stirrup, the third tiny bone that passes vibrations through the ear.
6. From the stirrup, the vibrations pass to the oval window. 
   
7. The oval window passes the vibrations to the cochlea. The cochlea is filled with liquid that moves when the

Nerve cells(neurones)

The motor neurones carry impulses from the central nervous system to muscles and glands.The sensory neurones carry impulses from the sense organs to the central nervous system.The multi-polar neurones are neither sensory nor motor but make connections to other neurones inside the central nervous system.A nerve can carry many different impulses.These impulses will travel in one direction in sensory fibres and in the opposite direction in motor fibres.The fibres run inside the nerve.    Synapse:at a synapse,a branch at the end of one fibre is in close contact with the dendrite of another neurone.When an impulse arrives at the synapse,it releases a tiny amount of a chemical substance called neurotransmiters wich sets off... Continue reading "true for me" »

archaea, extremophiles, cyanobacteria, bacteria.

DNA is the molecule that gives cells and organisms their biological characteristics. Types of Nucleotides: Adenine, Cytosine, Thymine, Guanine. DNA/RNA: DNA has a double helix structure, while RNA does not. In DNA, thymine is present, whereas in RNA, uracil is present. RNA can exit the nucleus, but DNA cannot. Ribose Nucleotide does not contain thymine. Transcription is the process of copying a part of the genetic message from DNA to RNA. Translation is the process in which RNA moves from the nucleus to the cytoplasm. Genetic Code refers to the relationship between the sequence of nitrogenous bases in DNA and the sequences of amino acids that form proteins. Transcription occurs in the nucleus, while translation occurs in the cytoplasm. In prokaryotic... Continue reading "DNA and Genetic Engineering: A Comprehensive Overview" »

Peripheral Nervous System

Consists of nerves and supports it collects info about the body's external and internal environment.

Central Nervous System

Consists of the brain and spinal cord, processes info, and creates a response.

Cell Body

The largest part of the typical neuron.

Dendrites

Short branched extensions that receive impulses from other neurons and carry them to the cell body.

Axon

Long fiber that carries impulses away from the cell body.

Myelin Sheath

Insulating membrane that surrounds a single, long axon.

Resting Potential

Electrical charge across the cell membrane of a resting neuron.

Action Potential

A nerve impulse that charges more negatively charged to more positively charged.

Threshold

The minimum level of a stimulus that is required to cause... Continue reading "Understanding the Nervous System and Sensory Organs" »

Elastic Fibers

Elastic fibers maintain the position of alveoli and bronchioles. When fibers recoil during exhalation, they reduce the size of alveoli and push air out.

Pneumocyte Type I

Pneumocyte type I cells are squamous epithelial cells that are unusually thin, providing an ideal site for gas diffusion.

Pneumocyte Type II

Pneumocyte type II cells are scattered among the squamous cells and produce surfactant.

Breathing

Deep breathing, also known as diaphragmatic breathing, involves the contraction of the diaphragm to change the volume of the lungs, allowing air to be exhaled passively. Shallow breathing, or costal breathing, occurs when the rib cage alters its shape, changing the thoracic volume.

Dalton's Law

Dalton's Law states that the partial pressure... Continue reading "Elastic Fibers and Gas Exchange in the Respiratory System" »