Stimuli, Responses, and Reproduction in Plants and Animals
Stimuli and Responses in Living Things
How Living Things Respond to Stimuli
Behavior is the sequence of actions triggered by a stimulus that causes a response. The organs producing a response are called effectors.
Movement: Predominantly in animals, involving muscle contractions.
Production of Substances: Glands produce secretions like sweat, saliva, and tears.
Responses in Plants
Tropisms: Changes in the direction of plant growth.
- Positive Tropism: Growth towards the stimulus.
- Negative Tropism: Growth
Understanding the Structure and Function of Cells
Cells: Exploring the Building Blocks of Life
Cell Structures and Their Functions
Eukaryotic Cells
Eukaryotic cells are characterized by a distinct nucleus enclosed within a membrane. These cells also contain various organelles, each with a specific role:
- Mitochondria: Double-membraned organelles responsible for energy production through cellular respiration.
- Nucleus: Houses the cell’s genetic material (DNA) organized into chromosomes.
- Golgi Apparatus: Processes and packages proteins and lipids.
- Cytoplasm:
Origin and Evolution of Life
1. Origin of Life
1.1 What is a Living Being?
– All living things are organized around something called a cell.
– In human beings, there are six main chemical elements: C, H2O, N2, P, S.
– The organic molecules are:
- Carbohydrates (containing C, H2, and O)
- Lipids (containing C, H2, and O)
- Proteins (C, H2, O, N2, S)
- Nucleic acids (C, H2, O, N2, P)
1.2 The Germinal Theory
Spontaneous Generation Theory: Human beings may appear from inanimate matter.
Pasteur (1822-1895): He demonstrated that living organisms could
Plant and Animal Tissues: Structure and Function
Plant Tissues
1. Meristematic Tissues
These small, polyhedral cells have thin walls, few vacuoles, and are found in apical and lateral meristems.
Apical Meristems
Responsible for primary growth (lengthening) at the tips of roots and stems.
Lateral Meristems
Responsible for secondary growth (thickening). Two types:
- Vascular Cambium: Produces vascular tissues.
- Cork Cambium: Produces cork (suber).
2. Permanent Tissues
Organized into three systems:
Ground System
- Parenchyma: Living cells.
- Collenchyma: Living cells
Nucleic Acids: DNA and RNA Structure and Function
Nucleic Acids: Components
DNA
Deoxyribonucleic acid (DNA) is a macromolecule composed of nucleotide chains. It consists of two nucleotide chains. The base pairs are adenine (A) with thymine (T), and guanine (G) with cytosine (C). DNA is highly conserved across organisms, with the exception of some viruses. In eukaryotic cells, DNA resides within the nucleus. In prokaryotic cells, it’s found freely in the cytoplasm. In chloroplasts and mitochondria, DNA is associated with histone-like proteins, similar
Read MoreMeiosis: The Cell Division Process for Sexual Reproduction
Meiosis: The Cell Division for Sexual Reproduction
Introduction
Sexual reproduction generally involves two parents and two key processes: fertilization and meiosis. Fertilization combines the genetic material of both parents, creating a new genetic identity for the offspring. Meiosis is a specialized type of nuclear division that redistributes chromosomes, resulting in haploid cells (n). Fertilization then restores the diploid chromosome number (2n).
Meiosis and Genetic Variability
Each haploid cell
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