This document discusses the key levels of biological organization from atoms to ecosystems. It outlines common features of living organisms including cells, growth, energy use, regulation, movement, response to stimuli, order, and reproduction. Evolution is presented as the core theme, with Darwin's theory of natural selection explained. The five kingdoms of life are described. Producers, consumers, and decomposers are explained as interdependent groups. Finally, the scientific method is summarized as a systematic approach involving observation, questioning, hypothesis, experimentation, and theory building.

1. Human Biology
Dr. jassim Mohammed Abdo
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Chapter 1

2. Biology: The study of life.
Greek origin:
Bio: Life
Logos: Study of

3. I. Life is based on many structural levels
Levels of biological organization:
– Atoms
– Molecules
– Subcellular organelles
– Cells
– Tissues
– Organs
– Organ systems
– Organism: May consist of a single cell or a
complex multicellular organism.

4. Levels of organization beyond organism:
• Population: Group of organisms of the same species that
interact with one another.
• Community: Several different populations living
together in same area (e.g.: lake, forest, jungle).
• Ecosystem: Interactions of community with non-living
environment (air, water, soil).
• Ecosphere: All ecosystems on planet earth. Includes:
– Biosphere: All biological communities on earth.
– Atmosphere (air)
– Hydrosphere (water)
– Lithosphere (crust)

5. Common features of all organisms:
1. Cells: Basic structural and functional unit of
life. Genetic information contained in DNA.
2. Growth and Development:
• Growth: Occurs by an increase in cell size, cell
number, or both.
• Development: Changes that take place during an
organism’s life.
3. Energy use and metabolism:
• All organisms must take in and transform energy to
do work, to live.
• Metabolism: All chemical reactions and energy
transformations essential for growth, maintenance,
and reproduction.

6. 4. Regulation
• External environment may change, but internal
environment remains fairly constant.
– Homeostasis: Organisms constantly strive to maintain a
“steady state” (e.g.: constant body temperature or blood pH)
despite changes in the internal and external environment.
– Metabolism is regulated by homeostatic mechanisms.
5. Movement:
• Internal movement: Characteristic of all life.
• Locomotion: Self-propelled movement from point A to
point B. Not observed in all life forms.
6. Respond to environmental stimuli: Organisms
respond to internal and external changes (visual
stimuli, temperature, light, sound, pressure, etc.).

7. 7. Order: Organisms are highly organized,
when compared to nonliving environment.
8. Reproduction: Organisms come from other
organisms. Reproduction may be sexual or
asexual.
9. Evolutionary adaptation: Populations, not
individuals, “evolve” or change over many
generations so they can survive in a changing
world.

9. Evolution is the core theme of biology
– Charles Darwin: Wrote “On the Origin of
Species by Means of Natural Selection” (1859)
in which he proposed the theory of evolution.
Evidence that led to the principle of evolution:
– Fossils: Most species that ever existed are
extinct; appear to be gradual progression
– Artificial selection of domestic/farm animals
– Adaptations: Organisms appear uniquely
suited to their environment (especially in
Galapagos).
• Darwin’s finches are a classic example

10. The theory of evolution by natural selection:
1. Genetic Variation: Due to genetic differences
there is variation within a population (size, color,
structure, etc.). These differences can be passed
on to an individual’s offspring.
2. Overproduction: Many more organisms are
born, than those that survive and reproduce.
3. Limits on population Growth: Limited
resources (food, water, space, sunlight, etc.)
creates competition
4. Differential reproduction: Organisms with
features that help them compete will be more
likely to survive and reproduce.

11. Natural Selection Changes Populations

12. Theory of evolution by natural
selection:
Consequences of natural selection
Over time, the characteristics of a
population will “evolve” and assume those
features that are “naturally selected”.
What is the heritable molecule with the
blueprints for the traits of an organism?
–DNA: Deoxyribose nucleic acid

13. All life can be classified taxonomically
– Taxonomy: The branch of biology concerned with
naming and classifying organisms
– Most Biologists Recognize Five Kingdoms: Monera,
Protista, Plantae, Fungi, and Animalia
1. Kingdom Monera (Procaryotae): Most widespread
organisms.
• Procaryotes (“Before nucleus”):
– Lack nuclear membrane around DNA.
– Lack membrane bound organelles (mitochondria, chloroplast,
golgi, endoplasmic reticulum).
• Unicellular: Single celled organisms.
• Have a cell wall.
• Include: Bacteria.

14. Kingdom Prokaryotae: Bacteria lack
nucleus and membrane bound organelles

15. Five Kingdoms of Living World:
2. Kingdom Protista:
• Eucaryotes (True nucleus):
– Have nuclear membrane around DNA.
– Have membrane bound organelles (mitochondria,
chloroplast, golgi, endoplasmic reticulum).
• Unicellular or simple multicellular.
• Most are larger and more complex than bacteria.
• Some have cell walls, others don’t.
• Some make their own food (phothosynthetic), others
must eat other organisms.
• Include: Protozoa, algae, slime molds.

16. Kingdom Protista: Eucaryotic Unicellular or
Simple Multicellular Organisms

17. Five Kingdoms (Continued):
3. Kingdom Fungi:
• Most are multicellular.
• Eucaryotes:
– Have nuclear membrane around DNA.
– Have membrane bound organelles (mitochondria,
chloroplast, golgi, endoplasmic reticulum).
• Have cell walls.
• Heterotrophs: Obtain food from other organisms.
• Most are decomposers, which absorb food from
dead organisms.
• Include: Mushrooms, yeasts, and molds.

18. Five Kingdoms (Continued):
4. Kingdom Plantae:
• Complex multicellular organisms.
• Cellulose cell walls.
• Eucaryotes: Have nuclear membrane around DNA
and membrane bound organelles.
• Autotrophs: Convert sunlight, water, and carbon
dioxide into food through photosynthesis.
• Other features:
– Waxy cuticle that prevents water loss.
– Multicellular sex organs.
– Openings in leaves and stems for gas exchange (stomata).
• Include: Trees, flowering plants, and mosses.

19. Five Kingdoms (Continued):
5. Kingdom Animalia:
• Complex multicellular organisms.
• Lack cell walls.
• Eucaryotes: Have nuclear membrane around DNA
and membrane bound organelles.
• Heterotrophs: Obtain chemical energy from living
sources..
• Features of complex animals:
– High degree of tissue specialization and body
organization.
– Locomotion.
– Well developed sense organs, nervous system, and
muscles.
• Include: Sponges, worms, insects, and vertebrates.

21. Interdependence of Biological Groups
1. Producers or Autotrophs:
• Self-nourishing organisms (plants, algae, etc.).
• Produce food from simple raw materials.
• Most carry out photosynthesis:
CO2 + H2O + Sunlight -----> Food + Oxygen
• Depend on nonproducers for carbon dioxide
2. Consumers
• Mainly animals.
• Heterotrophs that obtain food directly or indirectly
from producers.
• Carry out cellular respiration:
Food + Oxygen -----> CO2 + H2O + ENERGY
Gas exchange between producers and consumers helps
maintain balance of life-sustaining gases in atmosphere.

22. Interdependence of Biological Systems
3. Decomposers:
• Some bacteria, fungi, and animals.
• Recycle nutrients by breaking down products and
bodies of dead organisms.
• Process is vital because makes nutrients available
for use by other organisms.
• All organisms interact with each other and the
environment they live in.
• Interactions between producers, consumers, and
decomposers are essential to maintain proper conditions
for life on earth.

24. SCIENCE AS A METHOD OF INVESTIGATION
Scientia (Latin): To know
Science is a systematic way of thinking, answering
questions, and solving problems.
Steps of scientific method:
1. Observations
2. Question
3. Hypothesis
4. Predictions
5. Test predictions (Experiments)
Results of experiments may:
– Support (but not prove) hypothesis
– Disprove hypothesis -----> Change hypothesis.

25. Scientific method (Continued):
Hypothesis:
– Proposed explanation for observations
– An “educated guess”, should be consistent
with established facts
Variables in an Experiment
– Dependent Variable: What a scientist
measures.
– Independent variable: What a scientist
controls or manipulates.
– Standardized variables: What remains the
same throughout experiment. E.g.: Age, sex,
race, nutrition, health, etc.

26. Scientific method:
Replication
– Experiments are repeated numerous times.
– Consistent results increases confidence in results.
– Sample size: Larger sample sizes are generally better.
Theory:
– Hypothesis supported by a large body of observations and
experiments.
– Good theories relate previously unrelated facts and grow
as new information is obtained.
Principle:
– A theory that over time has yielded true predictions.
– Almost universally accepted.