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

Mitosis

Interphase: This is the state in which the cell is when it is preparing for division. During this time, the cell duplicates its genetic material, grows, and prepares the structures and proteins needed to carry out mitosis.

Prophase: This is the first phase of mitosis. During this phase, the cell's centrioles duplicate, and each pair moves to opposite poles of the cell. The nuclear membrane disintegrates. Chromosomes condense and become visible as double structures.

Metaphase: This is the second phase of mitosis. During this phase, the chromosomes align along the equatorial plane of the cell. The cytoplasmic spindle appears.

Anaphase: This is the third phase of mitosis. The chromatids separate and are pulled towards the spindle poles by... Continue reading "Cell Division: Mitosis, Meiosis, and Hormonal Regulation" »

Hormone Action

Endocrinology studies the glands of internal secretion, responsible for producing hormones, chemical messengers that act on tissues and organs of our body. The pituitary gland is controlled by hypothalamic releasing factors, the thyroid gland secretes thyroxine, the pancreas secretes insulin, the adrenal glands secrete adrenaline and cortisone, and the gonads secrete sex hormones.

Growth Hormone (GH or STH)

Growth hormone originates in the anterior pituitary gland and is considered essential for normal growth. It is classified as anabolic while under the influence of the diencephalic hormone STH. It is specific to the species, and its rate decreases after the age of 30.

Features:

• Stimulates growth and metabolic functions.
• Stimulates

Ecosystem Dynamics: Matter and Energy Flow

Flow of matter and energy in the ecosystem: Environmental inorganic compounds and organic matter are processed in photosynthesis, then returned to the environment and can be reused by producers. Plants transform solar energy, which is stored and then ceded to the environment, where it cannot be used by living things.

Types of Pyramids

Energy: Each rectangle represents the energy stored. The rectangle representing producers is always larger. Each trophic level provides sufficient energy to support the level above it.

Biomass: These pyramids are constructed using data on the amount of biomass at each trophic level. These pyramids can sometimes be reversed.

Numbers: These rectangles represent the number of... Continue reading "Ecosystem Dynamics: Matter, Energy, and Population Changes" »

Plasma Membrane: Structure and Function

The plasma membrane is a semipermeable, fluid, flexible, and selective membranous structure that surrounds the entire cell. It consists of a phospholipid bilayer (semipermeable), proteins (transport and structural), carbohydrates (cell communication), and cholesterol (structural). Its functions are to:

• Protect the cell
• Contain the cytoplasm and its organelles
• Maintain cell shape
• Establish communication between the cell and its environment
• Limit the cell
• Manage transport within the cell

Types of Transport

Passive Transport

Passive transport is a type of transport that does not require energy expenditure. However, it does require certain conditions.

a) Diffusion

Diffusion is the transport of substances through a semipermeable... Continue reading "Plasma Membrane: Structure, Function, and Transport Mechanisms" »

The Stages of Evolution and Speciation

The evolution of changes in living things that occur over time, leading to new species, can be distinguished in four stages:

1. Production of Evolutionary Change

   Natural selection favors certain individuals while harming others. Both still belong to the same species.

2. Genetic Isolation of the New Population

   To constitute a new species, it's imperative that members of the new species do not reproduce with the originals. This occurs when the new settlement becomes genetically independent. Various types of barriers include:

   • Geographical Barriers

     Prevent physical contact between populations (among individuals).

   • Sexual Barriers

     Due to anatomical differences that prevent mating or lack of synchrony in the fertile period,

Plant Waste Products

Gaseous substances: These include carbon dioxide and ethylene. Carbon dioxide is removed via stomata and lenticels, while ethylene is found in ripe fruits.

Liquid substances:

• Essential oils are expelled to the outside (ciliary ganglion) or stored (oleifera bags).
• Resins accumulate in the resin canals.
• Latex is stored within laticiferous channels.

Solid substances: Calcium oxalate accumulates as crystals in cell vacuoles.

Plant Respiration

Plants, like most living organisms, require oxygen for cellular respiration. As photosynthetic organisms, they also require carbon dioxide to synthesize their own organic matter. The addition of these gases does not require a respiratory apparatus as in animals, due to the following peculiarities:... Continue reading "Plant Waste, Respiration, and Vertebrate Urine Formation" »

Proteins

Proteins are polymers of amino acids, also known as polypeptides. They are essential biomolecules, as nearly all life depends on them.

Protein Structural Levels

Proteins can have thousands of amino acids, and therefore, their thousands of atoms can adopt a wide variety of positions. Importantly, a protein consists of thousands of amino acids linked one after another through peptide bonds, forming long linear chains. However, the final spatial structure of a protein is not a linear chain; it adopts a specific three-dimensional form in space, which is essential for its function.

Primary Structure

Consists of the amino acid sequence of a protein. It is the most basic and arguably the most important level of structural organization.

Secondary

Sexual Reproduction in Plants

Understanding the Process

Sexual reproduction is typical of plants with seeds. The reproductive organs are inside the flower, where gametes are produced. After pollination, fertilization and the formation of embryos and seeds take place. Pollination is the transfer of pollen grains from the anther of the stamen to the stigma of the pistil.

Flower Structure

A flower is the reproductive unit of a plant. It consists of the following parts:

• Calyx: Green sepals which protect the developing flower.
• Corolla: Brightly colored petals.
• Stamen: The male reproductive organ of the flower. It consists of a stalk (filament) and sacs (anthers), where pollen is stored.
• Pistil: The female reproductive organ of the flower. It consists of

Stem cells (or stem cells) are cells that have not completed their differentiation, either by being part of an embryo a few days old, or by being part of nature's reserves of immature cells in the adult organism.

Characteristics of Stem Cells

The key characteristics of stem cells are:

1. Self-renewal: The ability to produce more stem cells.
2. Differentiation: The origination of daughter cells of various types, which are converted by differentiation into specialized cell types.

Different Types of Stem Cells

Stem cells can be classified into the following types:

Totipotent Cells

There are about two hundred types of specialized cells, and all of them originate from unspecialized stem cells or differentiated cells. The first cell of every living thing, the... Continue reading "Stem Cells: Types, Characteristics, and Applications" »

The endosymbiotic theory explains the process of moving from a prokaryotic cell, which lacks most organelles, through symbiogenetic additions.

The Three Stages of Endosymbiosis

1. A bacterium that uses sulfur as an energy source merges with a swimming bacterium to form a new entity. The result was the first eukaryotic cell. The nucleoplasm of animal cells, plants, and fungi would be the result of the union of these two bacteria. A baseline characteristic of both cells was added: a new, more complex morphology. DNA remained confined to an inner core separated from the rest of the cell by a membrane.
2. This new organization was still anaerobic, unable to metabolize oxygen, as this gas was poisonous to it. Therefore, they lived in environments where oxygen,