Plant Embryo Development and Cellular Processes
Embryo Formation in Flowering Plants
The formation of embryos in flowering plants begins after fertilization, when the zygote (formed by the fusion of the male and female gametes) undergoes a series of divisions and differentiations. Though the initial stages of development are similar in both dicots and monocots, the final structure of the embryo differs significantly.
Dicot Embryo Formation
In dicot plants (e.g., bean, pea), the zygote first divides asymmetrically into a small terminal cell and a
Read MoreKey Concepts in Genetics: Gene, Locus, and Allele
Key Concepts in Genetics
The Gene
A gene is organized in a linear sequence of nucleotides in the molecule of DNA (or RNA in the case of some viruses), which contains the information necessary for the synthesis of a macromolecule with specific cellular function, usually proteins, but also mRNA, rRNA, and tRNA.
The Locus
In biology, a locus is a fixed position on a chromosome, the position of a gene or a genetic marker. A variant of the DNA sequence at a given locus is called an allele. The ordered list
Read MoreProtozoa and Porifera Characteristics and Classification
Phylum Protozoa: Primitive Unicellular Animals
Phylum Protozoa represents the most primitive group of animals, consisting of microscopic, unicellular organisms. Below is an examination of their general characteristics, classification, and a detailed look at the malaria parasite, Plasmodium.
1. General Characters of Phylum Protozoa
- Habit and Habitat: Mostly aquatic (freshwater or marine), but can also be found in damp soil. Many are commensals or parasites.
- Body Organization: Unicellular or acellular;
Molecular Biology and Genetics Fundamentals
Cellular Genetics and DNA Structure
Each cell of the body contains 23 pairs of chromosomes—46 in total—with 23 inherited from the mother and 23 from the father. Each chromosome contains genes, which consist of portions of DNA (Deoxyribonucleic acid). DNA is made up of nucleotides, which are the building blocks of both DNA and RNA. Nucleotides contain nitrogenous bases, and the sequence of these bases determines the differences in traits.
DNA exists as a double helix formed by two antiparallel
Read MoreCell Biology Timeline and Eukaryotic Cell Structure
Timeline of Key Cell Biology Discoveries
- 1590 – Hans and Zacharias Janssen built the first microscope.
- 1665 – Robert Hooke named the cell.
- 1670 – Anton van Leeuwenhoek designed a simple microscope.
- 1674 – van Leeuwenhoek discovered animalcules (bacteria and protozoa).
- 1838 – Schleiden started developing cell theory in plants.
- 1839 – Theodor Schwann extended cell theory to all animals.
- 1858 – Rudolf Virchow proved that all cells come from the division of pre-existing cells.
- 1888 – Santiago
Biology Exam Revision: Key Concepts in Physiology and Ecology
Factors Affecting Photosynthesis Rate
Point: Photosynthesis rate increases as light intensity, $\text{CO}_2$ concentration, and temperature increase—up to an optimum point.
Explanation:
- Light provides the energy for the light-dependent reactions.
- $\text{CO}_2$ is a necessary substrate for glucose synthesis (Calvin cycle).
- Temperature affects the activity of enzymes within the chloroplasts.
Example: In experiments, the rate of oxygen release (or $\text{CO}_2$ uptake) rises with light until a plateau