The Cell: History and Theory

• Biological Aspects of Public Health is the topic
• Sameen Noushad presents life sciences biology

What is Biology?

• Biology is the scientific study of living things
• Biologists define living things as all diverse organisms descended from a single celled ancestor around 4 billion years ago
• Living organisms share characteristics not found in non-living things

Characteristics of Living organisms

• Consist of one or more cells
• Contain genetic information
• Use genetic information to reproduce
• Are genetically related and have evolved
• They can convert molecules from their environment into new biological molecules
• Can extract energy from environment to use to do biological work
• Can regulate their internal environment

Hooke's Microscope

• In 1663, Robert Hooke observed a slice of cork using a microscope
• Cork is the bark of the cork oak tree, and made of cells that are no longer alive
• The empty spaces in the cork looked like tiny rectangular rooms
• Hooke called these empty spaces 'cells' which means "small rooms"

Leeuwenhoek's Microscope

• Microscopes were built in his spare time
• In 1674, he looked at drops of water, scrapings from teeth/gums, water from rain gutters
• It was surprising to him to find a variety of single celled organisms
• He called these moving organisms animalcules (meaning little animals)

Schleiden, Schwann, and Virchow

• In 1838, using his own and others research, Schleiden concluded all plants are made of cells
• Schwann reached the same conclusion with animals
• Virchow proposed that new cells are formed only from existing cells: "All cells come from cells"

Modern cell theory

• All organisms are made of one or more cells
• Cells are the basic unit of structure in all living things
• New cells arise from existing cells through cellular division
• Cells contain genetic material passed to daughter cells during cell division

Prokaryotes

• For more than 2 billion years after cells originated, all organisms consisted of only one cell
• These first unicellular organisms were prokaryotes
• Prokaryotic cells consist of DNA and other biochemicals enclosed in a membrane
• These prokaryotes were confined to oceans, where there was an abundance of complex molecules useable as raw materials and energy sources
• The ocean shielded them from UV, which was intense because there was little or no oxygen, hence no protective ozone layer

Photosynthesis

• Early on Earth there was no oxygen, so oxygen was toxic to existing life forms
• About 2.7 billion years ago photosynthesis changed the nature of life on Earth
• Photosynthetic prokaryotes became abundant, vast quantities of O2 slowly began to accumulate
• Oxygen was poisonous to many prokaryotes, but organisms that tolerated it could proliferate
• The presence of oxygen opened up new avenues of evolution

Eukaryotic cell evolution

• The endosymbiosis theory suggests that eukaryotic cells originated through a symbiotic relationship between prokaryotes
• The theory posits that certain organelles, like mitochondria and chloroplasts, were once free-living prokaryotes
• These prokaryotes were engulfed by a host cell, leading to a mutually beneficial relationship
• Engulfed prokaryotes provided the host cell with additional energy or the ability to perform photosynthesis
• The host cell offered protection and access to nutrients
• Eventually the prokaryote evolved into a eukaryote

Evolution

• As Schleiden and Schwann built the foundation for cell theory, Charles Darwin began to understand how organisms undergo evolutionary change
• Evolution is the process by which different kinds of living organisms are believed to have developed from earlier forms
• From 1831 to 1836, Darwin took part in a survey expedition by the ship HMS Beagle
• The HMS Beagle included stops in South America, Australia, and the southern tip of Africa
• At each stop, Darwin could study and catalog plants and animals

Discoveries related to evolution

• Darwin ended up at the Galapagos Islands and noticed that each island differed
• Some Galapagos Islands were rocky and dry, and some had better soil and more rainfall
• The plants and animals also differed from island to island

Galapagos tortoise evolution

• On drier islands, they had longer necks and a saddle like shell because they had to stretch to eat plants
• In humid areas where vegetation was abundant, the tortoises had a short neck and a dome shaped shell

Galapagos bird evolution

• It looks for insects under the bark of trees
• Feeds on insects and nectar
• Tears back bark in search of beetles
• Feeds on nectar
• Uses bill to crush seeds

Reproductive ability

• Organisms are capable of producing more offspring than their environments can support
• There is competition for limited resources in each generation
• Those offspring who meets the environmental criteria can survive
• Offspring will eventually die out without offspring

Survival of the fittest

• In a population, some individuals will have inherited traits that help them survive and reproduce
• Since the traits make them more effective at surviving and reproducing in that particular environment
• The individuals with the helpful traits will leave more offspring in the next generation than their peers,
• Any species with low fitness die and that with higher fitness can

Example of natural selection survival of fittest

• Mice Population moved to a new area where rocks very dark, so some black, some tan
• Tan mice are more visible to predatory birds than black mice with natural genetic variation
• Tan nice are more visible and eaten at higher frequency than black mice
• The surviving mice still leave some offspring in the new generation
• Because black has a higher chance of leaving they become more prevalent

Biological aspect of public health

• The World Health Organization defines public health as "the art and science of "preventing disease, prolonging life and promoting through the efforts of society
• Public health provides physical, social, and political conditions that empower people to gain control over the determinants of their own health
• Sound public health practice requires knowledge and understanding of health- and disease-related terminology, concepts and processes spanning the biologic spectrum This includes: cell, tissue, organ, system, and whole-body levels
• One should understand fundamental concepts of the disease process as they relate to important communicable and noncommunicable diseases that are observed globally

Determinants of health

• According to the "Health field" concept there are four major determinants of health
• Human Biology
  • Every human is mode of genes
  • Factors are genetically transmitted parents to offspring
  • There is a chance of transferring defective traits
  • Modern medicine has little help for these cases
• Environment
  • All which are external to individual human host
  • Environmental factors influence health, like water, air, climate, Rain fall, Crowding, income level
• Lifestyle or behavior
  • an action that has a specific frequency, duration, and purpose
  • Can also be unconscious
  • ex: Cigarette smoking, Unsafe sexual practice, and Eating contaminated food
• Health care organization
  • Health care organizations in terms of: resource in human power, equipments, and money

How biologists investigate life

• Scientists are guided by the scientific method, also called the hypothesis-prediction (H-P) method

1. making observations;
2. asking questions;
3. forming hypotheses, or tentative answers to questions;
4. making predictions based on the hypotheses; and
5. testing the predictions by making additional observations or conducting experiments

What is a hypothesis

• A hypothesis is an educated guess about the outcome of an experiment, based on existing knowledge/research
• Your hypothesis should be a clear and simple statement
• Your hypothesis should only state what you think your results will be
• An example of a hypothesis statement: "Bean plants will grow better in direct sunlight than in indirect sunlight or shade."
• It is unnecessary to say, "I think that" or "I believe", use If /Then

Example hypothesis scenario

• I decide to grow bean sprouts in my kitchen, near the windowsill, and wait for them to sprout
• After several weeks I have no seen sprouts
• The issue may be that I had forgotton to water the seeds
• Therefore, my hypothesis is: Bean seeds do not sprout if there is lack of water.

Experiments

• Scientists test their hypotheses using controlled experiments
• They are scientific tests done under controlled conditions:
• Only one (or a few) factors are changed at a time, while all others are kept constant
• A baseline must be established to see if treatment has effect
• Two groups must exist in the experiment, and are identical apart exception in the treatment one receives/one does not
• The group that receives the treatment in an experiment is called the experimental group
• The group that does not receive the treatment is the control group

Types of Variables

• Independent variable: the factor that is different between the control and experimental groups
  • The amount of water is known as the independent variable
  • It's an independent because it does not depend on the experiment, instead depends on the experimenter
• Dependent variable: the response that's measured to see if
  • The fraction of bean seeds that sprouted is known as the dependent variable
  • Depends on the amount of water, thus not independent variable

Water example variables

• The independent variable: amount of water
• Dependent Variable :The dependent variable: fraction of seeds that sprout

Practice independent and dependent variables example practice scenario

• A group of students were given a short course in speed-reading.
• The instructor wondered if a monetary incentive would influence performance on a reading test taken at the end of the course. Half the students were offered $5 for performance and other half were not
• The monetary incentive is the independent variable : ($5 or no money), this is the manipulated variable
• The Dependent variable is: performance on reading test
• $0 monetary incentive group is the Control Group : This group was not affected by the Independent Variable

Analysis and Conclusion

• After experiment, record the results and findings in an experiment and analyze those results
• You can record results within a data table or chart
• Data should be well organised so results/trends easier
• Take accurate + thorough measurements to validate data
• Find associations and trends through the connections of experiment and results
• State if you hypothesis has been disproved/approved

Analysis and Conclusion example

• After a week, nine out of ten seeds in the watered pot have sprouted, while none of the seeds in the dry pot
• The hypothesis is "seeds need water" and based on result is probably correct!

Explore cell history, theory, and the central role cells play in the structure and function of organisms. Review scientists' contributions from Hooke to cell theory.