Characteristics, Organization, and Transport in Organisms

Characteristics of Living Organisms

• Movement: This is defined as an action made by an organism causing a change of position or place.

• Respiration: These are chemical reactions that take place in cells that break down nutrient molecules and release energy for metabolism.

• Sensitivity: This is the ability to sense stimuli in the internal or external environment and make appropriate responses.

• Growth: This is a permanent increase in size and dry mass by an increase in cell number, increase in cell size, or both.

• Reproduction: This is the process that makes more of the same kind of organism.

• Excretion: This is the removal from organisms of waste products of metabolism, toxic materials, and excess substances.

• Nutrition: This is the process of taking in materials for growth, energy, and development.

Principles of Classification and the Binomial System

• All living things are classified under a specific hierarchy: Kingdom, Phylum, Class, Order, Family, Genus, and Species.

• Common Features of All Living Things: All living organisms share certain features, including the presence of:     

• Cytoplasm.     

• Cell membrane.     

• DNA (genetic material).     

• Ribosomes: These are found in the cytoplasm, either floating freely or attached to membranes called the rough endoplasmic reticulum. Ribosomes are responsible for making the proteins and enzymes involved in respiration.

• Species Definition: A group of organisms that can reproduce to produce fertile offspring.

• Binomial Naming System: It is a way to make classification standard worldwide.   The scientific name consists of two parts: the Genus and the Species.

• Format: The Genus starts with a capital letter, and the Species is all lower case. When written by hand, both parts should be underlined; when printed, they should be in italics. Example: Homo sapiens (the scientific name for humans).

• Rationale for Classification: Organisms are classified to identify those at risk of extinction and to understand evolutionary relationships.

• Methodology of Classification: Studying Morphology: The study of the form or outward appearance of organisms.

• Studying Anatomy: The study of internal structures by dissection.

• DNA and Protein Analysis: Sequences of DNA and amino acids in proteins provide a more accurate way of classification.

• Genetic Uniqueness: Each species has a unique number of chromosomes and a unique sequence of bases in its DNA. For instance, humans have $46$ chromosomes.

• Evolutionary Proximity: Organisms with recent ancestors have DNA sequences that are more similar than those that are distantly related.

• Linnaeus's System of Classification Hierarchy (From General to Specific):     1. Kingdom: Animalia     2. Phylum: Chordata     3. Class: Mammalia     4. Order: Primates     5. Family: Hominidae     6. Genus: Homo     7. Species: Sapiens

Whittaker’s Five Kingdom Scheme

The five kingdoms are Animal, Plant, Fungus, Prokaryote, and Protoctist.

Animal Kingdom:     

• Multicellular organisms.     

• Cells do not have a cell wall or chloroplasts.  

• Divided into groups such as Vertebrates and Arthropods.

Plant Kingdom:    

Multicellular organisms.     

Cells have a cell wall made of cellulose and contain chloroplasts with chlorophyll.     Autotrophic: They can make their own food.     Division - Ferns: Land-based plants that are vascular (possess xylem and phloem).         Undergo sexual reproduction.         

Produce gametes (sex cells) without seeds; the zygote becomes the fern plant directly.         

Have structures called sporangia which make spores.     

Division - Flowering Plants:   

Divided into Monocotyledons and Dicotyledons.    Feature Comparisons:             

Leaf Shape: Monocots have long and narrow leaves; Dicots have broad leaves.             

Leaf Veins: Monocots have parallel veins; Dicots have branching veins.             

Cotyledon: Monocots have one cotyledon; Dicots have two.             

Flower Grouping: Monocots group flowers in threes; Dicots group them in fives.

Fungus Kingdom:     

• Made up of thread-like structures called hyphae rather than traditional cells.     

• Many nuclei are distributed throughout the cytoplasm within the hyphae.     

• Examples: Yeast and Mushrooms.     

• Basic Fungal Cell Structure: Cell membrane, mitochondria, hyphae, fruiting body, and mycelium.

Prokaryote Kingdom:     

Unicellular organisms.     

Examples: Bacteria and algae.     

Lack a nucleus; chromosomes are not organized into a nucleus.     

Each bacterial cell contains a single chromosome consisting of a circular loop of DNA.  

Typical Bacterial Cell Structure:

Cell membrane, cell wall made from peptidoglycan, circular loop of DNA, plasmid (small rings of DNA containing extra genetic info), cytoplasm, ribosomes, and flagella/flagellum (for movement).

Protoctist Kingdom:     

• Unicellular organisms.     

• Possess a defined nucleus.   

• Example: Amoeba.

Viruses: Characteristics and Replication

• Structure: Viruses have a central core of RNA or DNA surrounded by a protein coat.

• Classification status: Virus particles are NOT cells. They do not feed, excrete, respire, or grow.

• Biological function: They lack a nucleus, cytoplasm, cell organelles, or cell membrane.

• Reproduction: They do reproduce, but only inside the cells of a living organism by using materials from the host cell.

Understanding and Identifying Organisms

• Dichotomous Keys: Used to identify organisms. Each key is made of contrasting features in a branching structure (Dichotomous means 2 branches)

Eukaryotic Cell Organization and Structure

• Eukaryotic cells possess a nucleus and membrane-bound organelles.

Shared Structures in Animal and Plant Cells:    

Cell Membrane: Selective control of what enters and leaves the cell.     

Nucleus: Carries internal genetic material.

Cytoplasm: A jelly-like substance where all chemical reactions occur.  

Ribosomes: The site of protein synthesis. Mitochondria: The site of aerobic respiration. Cells with high metabolism need many mitochondria to release energy.

Plant-Only Internal Structures:     

• Cell Wall: Provides structural support; made from cellulose.     

• Chloroplasts: The site of photosynthesis in plants.     

• Permanent Vacuole: Stores and isolates harmful materials; stores small nutrients; maintains water balance; provides structural support via turgor pressure.

• Differences in Animal Vacuoles: Some animal cells have vacuoles, but they are temporary, not central, and much smaller.

Specialized Cells and Their Adaptations

• Ciliated Cells: Found in the trachea and bronchi; have cilia (extensions of the cell membrane) that allow the movement of mucus.

• Root Hair Cells: Adapted for absorption; they have a root hair to increase surface area, thin walls, and a large permanent vacuole for storage. They contain no chloroplasts because they are underground.

• Neurons (Nerve Cells): Designed for the conduction of impulses; they are long to reach different parts of the body and have extensions/branches to connect to other cells. The axon is covered in a fatty sheath that insulates the cell and speeds up the nerve impulse.

• Red Blood Cells: Specialized for oxygen transport. They have a biconcave shape for increased surface area and flexibility. They contain haemoglobin to join with oxygen. They contain no nucleus to increase oxygen-carrying capacity.

• Palisade Mesophyll Cells: Specialized for photosynthesis; they have a column shape to maximize sunlight absorption and fit many cells in one layer. They contain a high concentration of chloroplasts.

• Sperm Cells: The head contains a haploid nucleus with genetic info and an acrosome with digestive enzymes to penetrate the egg. The mid-piece contains many mitochondria for swimming energy, and a tail allows for movement.

• Egg Cells: Feature lots of cytoplasm for nutrients and the growth of the embryo. The cell membrane changes after fertilization to prevent more sperm from entering.

Levels of Biological Organization and Division

• Level 1 - Cell: The basic functional and structural unit in living organisms.

• Level 2 - Tissue: Groups of cells of similar structure working on the same function.

• Level 3 - Organ: Made from different tissues working together to perform a specific function.

• Level 4 - Organ System: Groups of organs with related functions working together to perform specific functions.

• Growth and Repair: Cells in the body need to divide to allow for growth and repair. New cells are produced through the division of existing cells.

Measuring Specimens and Magnification

• The formula for magnification is expressed as: $\text{Magnification} = \frac{\text{Image size}}{\text{Actual size}}$.

• Calculations for actual size ($A$), image size ($I$), and magnification ($M$) follow the triangle formula: $I = A \times M$.

• Units and Conversions: Magnification has no units. To convert from millimeters to micrometers: $1\,mm=1000\,mm$.

• Practical Example:     - Image size = $50\,mm$     - Actual size = $2000\,mm$     

• Step 1: Convert actual size to mm: $\frac{2000}{1000} = 2\,mm$   

• Step 2: Calculate magnification: $\frac{50\,mm}{2\,mm} = 25$     

• Final Magnification = $25$ (no unit)

Movement of Substances: Diffusion

• Definition: The net movement of particles from a region of higher concentration to a region of lower concentration as a result of random movement.

• Mechanism: Energy for diffusion is sourced from the kinetic energy of the random movement of particles. Particles move down a concentration gradient until they are spread evenly in all spaces.

• Importance in Animals: Gas exchange ($O_2$, $CO_2$) and the absorption of dissolved food materials.

Importance in Plants: Gas exchange ($O_2$, $CO_2$) during photosynthesis and the diffusion of dissolved salts through root hair cells.

Factors Influencing Diffusion Rate:     

• Surface Area: A larger surface area of the exchange membrane allows faster diffusion.

• Temperature: Higher temperatures increase kinetic energy, leading to faster particle movement.     

• Concentration Gradient: A steeper gradient (greater difference between low and high concentrations) results in faster diffusion.

• Distance: A thinner exchange membrane makes it easier for particles to pass through, increasing the rate.

Movement of Substances: Osmosis

• Definition: The net movement of water molecules from a region of high water potential (dilute solution) to a region of lower water potential (concentrated solution) through a partially permeable membrane.

Mechanism: Occurs in both plant and animal cell membranes.

Effects on Plant Cells:     

• In Distilled Water: Water moves into the cell; the cell swells and becomes turgid. The cell wall prevents bursting. The vacuole exerts turgor pressure on the elastic wall.     

• In Salt Solution: Water moves out; the cell becomes plasmolyse (flaccid). If all cells in a leaf become flaccid, the plant wilts.

Effects on Animal Cells:     

In Pure Water: Excess water enters and if it is not expelled, the cell bursts (hemolysis).

In Salt Solution: Water osmoses out of the cytoplasm; the cell shrinks (becomes crenated).

• Tonicity Definitions:     

• Hypertonic: More salt/sugar than the cell.     

• Isotonic: Similar concentration of salt/sugar as the cell/blood.     

• Hypotonic: Less salt/sugar than the cell/blood.

• Biological Importance: Plants gain water via osmosis from soil to roots to stay firm and turgid. Animal cells are surrounded by tissue fluid, which typically has the same concentration as the internal cell liquid.

Active Transport

• Definition: The movement of particles through a cell membrane from a region of lower concentration to a region of higher concentration using energy acquired from respiration.

Mechanism: Specific carrier proteins pick up molecules and transport them against the concentration gradient. The substance combines with the carrier molecule. Energy from respiration provides the carriers the kinetic energy needed to change shape and move the substance through the membrane.

Biological Importance:    

•  Uptake of glucose by epithelial cells in the villi of small intestines.    

•  Uptake of glucose by kidney tubules in the nephrons.    

•  Uptake of ions from soil water by root hair cells in plants.