Notes, summaries, assignments, exams, and problems for Biology

Phases of Neuromuscular Transmission

Motor Neuron Transmission:

1. The action potential occurs in the axonal cone and travels along the axon (nodes of Ranvier). When it reaches the presynaptic membrane, voltage-gated Ca channels open.
2. Ca enters the neuron, and the presynaptic membrane attracts vesicles of acetylcholine (ACh) found in the axon's cytosol.
3. Acetylcholine is released into the synapse.
4. Chemical-gated channels open when coupled to ACh, allowing Na to enter the cell.
5. An action potential occurs in the muscle cell membrane and spreads throughout the plasmolemma.
6. In the triad, dihydropyridine receptors (DHPR) are close to the terminal cisternae. When stimulated by the action potential, they stimulate ryanodine receptors. Ryanodine receptors (calcium

Plant Tissue Systems

Plant tissues are responsible for growth and structure. They are broadly classified into meristematic and definitive tissues.

Meristematic Tissues

Meristematic tissues are responsible for plant growth. The cells are small, polyhedral in form, with thin walls and abundant small vacuoles initially.

• Apical Meristems: Responsible for primary growth in length of the plant. They are located at the ends of the root and stem.
• Lateral Meristems: Responsible for growth in girth or secondary growth. They are distributed throughout the plant. They produce vascular cambium (conducting tissue) and cork cambium (which gives rise to suber or cork).

Definitive Tissues (Fundamental Tissue System)

Definitive tissues are specialized and typically... Continue reading "Plant Tissue Systems and Types" »

Understanding the Complement System

Among the factors that may act on both the Alternative Complement pathways and lectins are:

• C3 Factor I
• C2 C4

The Complement system factors that can act with serine protease activity are:

• Bb / Factor I
• MBL / C2

Complement Factors and Their Derivatives

Regarding complement factors or their derivatives:

• C3b can act as an opsonin
• Anaphylatoxin C4a
• C5a is a chemotactic agent
• C2a is an inflammatory agent
• C3b helps elimination of immune complexes
• C1r is a serine protease

Opsonization

Opsonization is a phenomenon that may be immune mediated by:

• C4b
• MBL
• IgG
• C3b

Classical Pathway of Complement Activation

Key aspects of the classical pathway of complement activation:

• It is associated with the adaptive immune response.
• It is activated by an

Sympathetic Nervous System (SNS) vs. Parasympathetic Nervous System (PNS)

The Parasympathetic Nervous System (PNS) prepares the body for changes, influencing heart rate and respiration. The Sympathetic Nervous System (SNS) restores the body to a resting state.

Nervous System Cells

• Neurons: The basic units of the Central Nervous System (CNS) and the peripheral nervous system.
• Glial cells: Support cells within the nervous system.

Peripheral Nervous System

The peripheral nervous system forms neural networks.

• Soma (neuronal body): Contains the cell nucleus and organelles. It provides energy to the cell. Lysosomes degrade cellular waste.
• Dendrites: Branching extensions that receive signals from other neurons.
• Axon: A long, slender projection that conducts

Brain Protection and General Composition

The brain is enclosed and protected by the skull. Beneath the skull, the meninges provide further protection, and Cerebrospinal Fluid (CSF) flows within this space to reduce friction and cushion the brain.

The brain consists of two main types of tissue: gray matter and white matter.

• Gray Matter: Primarily involved in processing information and generating responses. It has a cortical arrangement (forming the outer layer or cortex) and is also found in deeper clusters called nuclei.
• White Matter: Forms a large mass connecting different brain areas. The corpus callosum, a large white matter structure, connects the two cerebral hemispheres across the interhemispheric fissure.

Important functions are associated... Continue reading "Human Brain Anatomy: Structure and Function" »

The Cells and Tissues of Plants

Plant Cell: Plant cells have eukaryotic cell structures except for the animal centrosome and possess a cell wall surrounding the membrane. They have chloroplasts and vacuoles.

Cell Types

Parenchymal Cells: These cells secrete substances and store hormones. They can undergo differentiation to perform specific functions, such as tracheids, which die and become woody vessels to circulate crude sap.

Simple and Complex Tissues

Tissues are groups of cells that perform a specific activity. They are classified according to the number of cell types (one or more) into simple and complex tissues.

• Simple Tissues: Parenchyma, collenchyma, and sclerenchyma.
• Complex Tissues: Formed by different cell types performing various functions,

Blood Circulation and Waste Removal Processes

The exchange of substances occurs between blood plasma and tissue cells through a network of arteries and veins.

The Heart's Chambers

Atria

The atria receive blood from the veins coming from the body's organs. They communicate with the ventricles through valves (mitral and tricuspid).

Ventricles

The ventricles are connected to arteries that pump blood from the heart throughout the body. Semilunar valves between the ventricles and arteries prevent backflow.

Blood Flow Dynamics

Blood always flows in the same direction: from veins to arteries.

• Atrial Systole: Atrial contraction pushes blood into the ventricles.
• Ventricular Systole: Ventricles contract, closing the mitral and tricuspid valves, and forcing blood

Arteries and Superficial Veins of the Skull and Face

Neck Origin:

• **Arteries:** Common carotid, internal and external carotid.
• **Veins:** Internal and external jugular vein.

Jugular Vein Origin:

• Retromandibular vein (posterior to the jaw)
• Posterior auricular vein (behind the ear)
• Occipital vein (in the occipital region)
• Emissary vein (by the occipital region)
• Parietal emissary vein (parietal and occipital region)
• Nasofrontal vein (frontal nose and region)
• Dorsal nasal vein
• Zygomaticotemporal vein
• Angular vein (eye)
• Zygomaticofacial vein
• Infraorbital vein

Carotid Artery Origin:

• Posterior auricular artery
• Occipital artery
• Anterior auricular artery
• Superficial temporal artery
• Zygomatico-orbital artery
• Supraorbital artery
• Supratrochlear artery
• Dorsal nasal artery
• Zygomaticotemporal

Subclavian Artery

The subclavian artery is divided into three portions: pre-scalenic, intra-scalenic, and post-scalenic. It originates several branches:

• Vertebral Artery: Both vertebral arteries join to form the basilar artery, which contributes to the posterior cerebral circulation.
• Internal Thoracic Artery: Gives off mediastinal branches, thymic branches, bronchial branches, the pericardiacophrenic artery, sternal branches, perforating branches, lateral costal branches, and anterior intercostal branches. The internal thoracic artery then divides into the musculophrenic artery and the superior epigastric artery.

Thyrocervical Trunk

The thyrocervical trunk gives rise to:

• Inferior Thyroid Artery: Which further branches into the inferior laryngeal

DNA vs. RNA: Key Differences

DNA (Deoxyribonucleic Acid)

• Composition: The pentose sugar is D-deoxyribose. Contains the nitrogenous bases Adenine (A), Guanine (G), Thymine (T), and Cytosine (C) in similar proportions.
• Structure: DNA is a double-stranded molecule consisting of two polynucleotide chains.
• Configuration: Forms a double helix structure with the two chains connected by base pairing (A-T and C-G).
• Location: In eukaryotic cells, DNA is located in the nucleus, forming chromosomes. In prokaryotic cells, it forms a single, circular chromosome located in the cytoplasm.
• Function: DNA encodes the information that determines the order of amino acids required to synthesize all cellular proteins. A gene, a defined segment of DNA, contains the information