BIO 101 Note – General Biology 1

BIO 101: GENERAL BIOLOGY 1 (2024/2025 SESSION)

(A) EVOLUTION

Introduction

Evolution is the process by which organisms change over generations through genetic variation and natural selection. The study of the evolution of plants and animals helps us understand biodiversity, adaptation, and the complexity of life forms. This lecture will cover the origins, classification, and evolutionary trends of plants and animals.

1. Evolution of Plants

1.1 Origin of Plants

Plants are believed to have evolved from green algae (charophytes), which are simple aquatic organisms. The transition from water to land required significant adaptations such as the development of roots, vascular tissues, and reproductive strategies to prevent desiccation.

1.2 Major Evolutionary Stages

1. Algal Ancestors (Proterozoic Era):

• The Proterozoic Era spans from 2.5 billion years ago (bya) to 541 million years ago (mya).

• It is the longest era of the Precambrian time and is significant for several key developments in the history of life on Earth.

• The earliest photosynthetic organisms were cyanobacteria, followed by algae.

2. Bryophytes (Non-vascular Plants):

• Mosses and liverworts were among the first land plants, relying on water for reproduction.

3. Pteridophytes (Ferns and Relatives):

• The development of vascular tissues (xylem and phloem) allowed for increased size and water transport.

4. Gymnosperms (Cone-bearing Plants):

• Plants like conifers developed seeds for reproduction, reducing dependency on water.

5. Angiosperms (Flowering Plants):

• The most advanced group, characterized by flowers, fruits, and efficient pollination mechanisms.

1.3 Adaptations of Plants to Different Environments

• Xerophytes: Plants adapted to dry conditions (e.g., cacti: Carnegiea gigantea, Opuntia spp.).

• Hydrophytes: Aquatic plants with special adaptations (e.g., water lilies).

• Mesophytes: Plants that thrive in moderate conditions (e.g., most trees and shrubs).

2. Evolution of Animals

2.1 Origin of Animals

Animals evolved from unicellular eukaryotes likely similar to modern protists (choanoflagellates). The transition from unicellular to multicellular life marked a significant evolutionary milestone.

Unicellular eukaryotes are organisms that consist of a single cell with a well-defined nucleus and other organelles that carry out specific functions; their genetic materials are enclosed within a membrane-bound nucleus.

Some examples of other unicellular eukaryotes are:

1. Amoeba (Amoeba proteus) – A shapeless, free-living protozoan found in freshwater.

2. Paramecium (Paramecium caudatum) – A ciliate protozoan that moves using cilia.

3. Euglena (Euglena gracilis) – A mixotrophic organism capable of photosynthesis and heterotrophic feeding.

4. Plasmodium (Plasmodium falciparum) – The parasite responsible for malaria.

5. Trypanosoma (Trypanosoma brucei) – Causes African sleeping sickness.

6. Yeast (Saccharomyces cerevisiae) – A unicellular fungus used in fermentation and baking.

7. Giardia (Giardia lamblia) – A parasitic protozoan that causes giardiasis, an intestinal infection that leads to diarrhea and stomach cramps. It spreads through contaminated water and animals.

8. Toxoplasma (Toxoplasma gondii) – Found in warm-blooded animals, especially cats, and can be transmitted to humans, causing toxoplasmosis, which is harmful, especially to pregnant women and people with weakened immune systems.

9. Entamoeba histolytica – Moves using pseudopodia. It causes amoebic dysentery, an infection leading to severe diarrhea, abdominal pain, and other gastrointestinal issues.

2.2 Major Evolutionary Stages of Animals

1. Precambrian Life (600 million years ago) – Soft-bodied, simple organisms like sponges.

2. Cambrian Explosion (~540 million years ago) – Rapid diversification of animal life, leading to the emergence of major phyla such as arthropods and mollusks.

3. Fish and Amphibians (Paleozoic Era) – The first vertebrates appeared, followed by amphibians adapting to land.

4. Reptiles and Mammals (Mesozoic Era) – Reptiles dominated, and mammals began evolving.

5. Birds and Advanced Mammals (Cenozoic Era) – Mammals diversified, leading to the rise of primates and ultimately humans.

2.3 Adaptations of Animals

• Aquatic Adaptations – Gills in fish, streamlined bodies in whales.

Terrestrial Adaptations:

Lungs, limbs for movement, and water retention mechanisms in reptiles.

Aerial Adaptations:

Hollow bones and feathers in birds for flight.

3. Evolution and Human Health

Understanding evolution is crucial in health sciences because it explains:

• The emergence of drug-resistant bacteria and viruses.

• Human anatomical and genetic adaptations.

• Evolutionary origins of diseases.

(B) Natural Selection

Natural selection is a fundamental concept in evolutionary biology that explains how species evolve over time. It was first proposed by Charles Darwin in his 1859 book, On the Origin of Species.

Natural selection is a process by which individuals with advantageous traits survive and reproduce more successfully than others in their environment. Over generations, these beneficial traits become more common in the population, leading to evolutionary change.

Principles of Natural Selection

Natural selection operates based on the following key principles:

1. Variation: Within any population, individuals exhibit differences in traits such as size, color, resistance to disease, and reproductive success.

2. Differential Survival and Reproduction: Individuals with favorable traits are more likely to survive, reproduce, and pass on their genes.

3. Adaptation: Over time, populations become better suited to their environment as beneficial traits accumulate.

4. Heritability: Traits that confer advantages must be heritable, meaning they can be passed from parents to offspring.

Traits that confer advantages in a population of organisms are called adaptive traits because they improve an organism’s chances of survival and reproduction. These traits can be classified into structural, physiological, and behavioral adaptations. Here are some examples:

a. Structural (Morphological) Traits

These are physical characteristics that help an organism survive in its environment.

• Camouflage in chameleons and stick insects – Helps them avoid predators.

• Thick fur in Arctic foxes and polar bears – Provides insulation in cold climates.

• Long necks in giraffes – Allow them to reach high tree leaves for food.

• Webbed feet in ducks and frogs – Aid in swimming efficiently.:

b. Physiological (Functional) Traits

These are internal processes or biochemical adaptations that help an organism survive.

• Venom in snakes and spiders – Used for hunting and defense.

• Hibernation in bears – Allows survival during food-scarce winters.

• Salt tolerance in mangrove trees – Enables them to grow in coastal environments.

• Heat resistance in bacteria (e.g., Thermophiles) – Allows survival in extreme temperatures.

c. Behavioral Traits

These are actions or behaviors that improve an organism’s chances of survival and reproduction.

• Migration in birds and wildebeests – Helps them find food and suitable breeding grounds.

• Hunting in packs (wolves, lions) – Increases hunting success.

• Playing dead (opossums, some insects) – Helps avoid predation.

• Tool use in primates and crows – Increases efficiency in acquiring food.

Each of these traits provides a selective advantage, increasing an organism’s ability to survive, reproduce, and pass on its genes to the next generation.

Types of Natural Selection

There are three main types of natural selection:

1. Directional Selection: This occurs when one extreme of a trait is favored.

Example: In a population of bacteria, those with resistance to antibiotics survive and multiply, leading to an increase in resistant strains.

2. Stabilizing Selection: This favors the average traits in a population and eliminates extreme variations.

Example: In human birth weight, babies that are too small or too large have higher mortality rates, leading to the prevalence of moderate birth weights.

Low Birth Weight (Too Small)

• A baby is classified as low birth weight (LBW) if they weigh less than 2,500 grams (2.5 kg or 5.5 pounds) at birth.

• Very low birth weight (VLBW): Less than 1,500 grams (1.5 kg or 3.3 pounds).

• Extremely low birth weight (ELBW): Less than 1,000 grams (1 kg or 2.2 pounds).

Risks of Low Birth Weight:

• Higher risk of infections, breathing difficulties, and developmental issues.

• More common in premature babies (born before 37 weeks of pregnancy).

Normal Birth Weight (Healthy Range)

• A healthy full-term baby typically weighs between 2.5 kg (5.5 lbs) and 4.0 kg (8.8 lbs).

High Birth Weight (Too Large)

A baby is classified as macrosomic (large for gestational age, LGA) if they weigh more than 4,000 grams (4 kg or 8.8 pounds) at birth.

Some doctors consider 4,500 grams (4.5 kg or 9.9 pounds) as a more accurate threshold for macrosomia.

Risks of High Birth Weight:

• Difficult delivery due to the baby’s size (risk of birth injuries).

• Higher risk of low blood sugar (hypoglycemia) after birth.

• Increased likelihood of obesity and diabetes later in life.

Factors Affecting Birth Weight:

• Genetics (parents’ size).

• Maternal health (nutrition, diabetes, smoking, infections).

• Gestational age (premature babies are usually smaller, while post-term babies tend to be larger).

3. Disruptive Selection:

This favors individuals with extreme traits over those with intermediate traits.

Example: In some species of birds, those with either very large or very small beaks survive better than those with medium-sized beaks, depending on available food sources.

Examples of Natural Selection in Health and Medicine

Natural selection is crucial in health sciences and medicine. Some examples include:

• Antibiotic Resistance: Overuse of antibiotics has led to the emergence of resistant bacterial strains, such as Methicillin-resistant Staphylococcus aureus (MRSA).

• Sickle Cell Trait and Malaria Resistance: Individuals who inherit one sickle cell gene and one normal gene have a survival advantage in malaria-endemic regions, as the sickle cell trait provides resistance to Plasmodium infection.

• Lactose Tolerance: Some human populations have evolved the ability to digest lactose into adulthood due to the domestication of dairy animals.

Implications for Health Sciences and Medicine

Understanding natural selection helps health professionals:

• Develop better treatments for infectious diseases by anticipating microbial evolution.

• Predict how genetic disorders persist in populations.

• Improve public health strategies, such as vaccination programs that consider pathogen evolution.

BIO 101: GENERAL BIOLOGY 1

TOPIC: REPRODUCTION PROCESSES AND LIFE CYCLES IN PLANTS AND ANIMALS

Reproduction is a biological process by which organisms produce offspring to ensure the continuity of their species. It occurs in both plants and animals through various mechanisms, classified broadly into asexual and sexual reproduction. The life cycles of organisms vary depending on their reproductive strategies and environmental adaptations.

Reproduction in Plants

1. Types of Plant Reproduction

Asexual Reproduction

Asexual reproduction in plants does not involve the fusion of gametes. Offspring are genetically identical to the parent plant (clones). Common types include:

• Vegetative Propagation: New plants arise from structures like stems, roots, and leaves.

• Examples: tubers (potato), bulbs (onion), and leaves (Bryophyllum sp.).

• Fragmentation: A part of the plant breaks off and develops into a new individual, as seen in algae like Spirogyra.

• Budding: A new plant develops as an outgrowth, commonly found in yeast and some bryophytes.

• Sporulation: Spores are formed and dispersed, germinating into new individuals (e.g., ferns and fungi).

Sexual Reproduction

Sexual reproduction in plants involves the fusion of male and female gametes, leading to genetic variation. It occurs in:

• Gymnosperms: Cone-bearing plants where seeds develop without an enclosing fruit (e.g., pine trees).

• Angiosperms: Flowering plants where fertilization occurs within flowers, producing seeds enclosed in fruits.

Reproduction in Algae

Algae exhibit both asexual and sexual reproduction, and the mode of reproduction varies depending on the species and environmental conditions.

Asexual Reproduction (Common in favourable conditions)

This occurs without gamete formation and results in genetically identical offspring. Common methods include:

• Binary Fission – A single algal cell divides into two daughter cells (e.g., Chlamydomonas).

• Fragmentation – The thallus breaks into smaller pieces, each growing into a new individual (e.g., Spirogyra).

• Spore Formation – Special asexual spores such as zoospores (motile) and aplanospores (non-motile) are released (e.g., Chlorella).

Sexual Reproduction (Occurs in unfavorable conditions)

This involves gamete fusion and leads to genetic variation. The types include:

• Isogamy – Fusion of two similar gametes (e.g., Ulothrix).

• Anisogamy – Fusion of two dissimilar gametes, where one is larger than the other (e.g., Eudorina).

• Oogamy – Fusion of a large, immobile egg and a smaller, motile sperm (e.g., Fucus).

3. Alternation of Generations (Common in multicellular algae)

Some algae, like brown and red algae, have a haplodiplontic life cycle, alternating between a haploid gametophyte and a diploid sporophyte phase (e.g., Polysiphonia).

2. Life Cycle of Flowering Plants

Flowering plants exhibit an alternation of generations, which includes:

• Sporophytic generation (Diploid): The dominant phase producing spores through meiosis.

• Gametophytic generation (Haploid): Produces gametes through mitosis, leading to fertilization and seed formation.

Typical life cycle of angiosperms takes the following steps below:

1. Pollination – Pollen (male gamete) is transferred to the stigma of a flower.

2. Fertilization – Pollen travels down the style to the ovary, where it fuses with an egg in the ovule.

3. Seed Formation – The fertilized ovule develops into a seed, while the ovary becomes a fruit.

4. Seed Germination – Under favorable conditions, the seed sprouts and grows into a seedling.

5. Vegetative Growth – The seedling matures into an adult plant with roots, stems, and leaves.

6. Flowering – The mature plant produces flowers, restarting the cycle.

The angiosperm life cycle typically demonstrates the alternation of generations with haploid gametophyte and diploid sporophyte alternation. The flower is the reproductive structure of an angiosperm and can be either unisexual or bisexual. One of its primary duties is to produce seeds through sexual reproduction. Also, double fertilization is a characteristic feature of angiosperms.

Fig. I: Typical life cycle of Angiosperms

Reproduction in Animals

1. Types of Animal Reproduction

Asexual Reproduction

This occurs in lower organisms and results in offspring genetically identical to the parent. Types include:
• Binary fission: One organism splits into two (e.g., Amoeba, Paramecium).
• Budding: An individual grows out of the body of the parent (e.g., Hydra).
• Fragmentation: An organism breaks into pieces, each regenerating into a new individual (e.g., starfish).

Parthenogenesis
• Development of an embryo from an unfertilized egg (e.g., some insects and reptiles).

Sexual Reproduction

Sexual reproduction involves the fusion of male and female gametes, leading to offspring with genetic diversity. It includes:
• External Fertilization: Gametes fuse outside the body, common in aquatic animals (e.g., fish, amphibians).
• Internal Fertilization: Gametes fuse inside the body, common in mammals, reptiles, and birds.

2. Life Cycles of Selected Animals

Insects
• Egg → Larva → Pupa → Adult (Complete metamorphosis: Butterfly)
• Egg → Nymph → Adult (Incomplete metamorphosis: Cockroach)

Amphibians (e.g., Frog)
• Egg → Tadpole (Aquatic) → Metamorphosis → Adult (Terrestrial)

Mammals (e.g., Humans)
• Fertilization → Zygote → Embryo → Foetus → Birth → Growth → Maturity → Reproduction

Significance of Reproduction and Life Cycles
1. Survival of species: Ensures species continuity and adaptation.
2. Genetic variation: Enhances adaptability and evolution (in sexual reproduction).
3. Population growth: Maintains ecological balance and food chains.

Conclusion

Reproduction is fundamental for the survival of plants and animals. While asexual reproduction ensures rapid population growth, sexual reproduction introduces genetic diversity necessary for adaptation. Understanding life cycles helps in conservation, agriculture, and medical sciences.