Introduction to Life Sciences PDF

Life’s Origin and Early Evolution LEARNING OBJECTIVES: 1.Explain the evolving concept of life based on emerging pieces of evidence. 2.Describe how unifying themes in the study of life show the connections among living things and how they interact with each other and with their enviro...

Life’s Origin and Early Evolution LEARNING OBJECTIVES: 1.Explain the evolving concept of life based on emerging pieces of evidence. 2.Describe how unifying themes in the study of life show the connections among living things and how they interact with each other and with their environment. What was the first form of life? Life is believed to have existed on Earth for billions of years now. Scientists do not know exactly when life began on Earth. However, they are able to trace how life developed and evolved using some pieces of evidence.  WHAT IS A CELL? Cell is the basic membrane-bound unit that contains the fundamental molecules of life and of which all living things are composed. CELL THEORY DISCOVERY OF CELLS Most cells cannot be seen with naked eye. So how were they first discovered? What was needed for their discovery? CELLS DISCOVERED ROBERT HOOKE (1665) Use basic microscope to look at thin slices of plant tissues– cork Looked empty, like monk’s chamber Called tiny chambers “cells”.  ANTON VAN LEEUWENHOEK 1676 was first to view pond water organisms was first to observe blood and sperm cells w/ microscope. introduced the first unicellular organisms w/c he called animalcules. Made careful sketches.  MATTHIAS SCHLEIDEN 1838 German botanist All plants looked at were made of cells. He concluded “ All plants are made of cells.”  THEODORE SCHWANN 1839 German scientist who studied animals– zoologist. Saw that all animals he studied were cellular. Concluded “All animals are made of cells.”  RUDOLF VIRCHOW 1858 German physician who studied cell reproduction “Where a cell exists, there must have been a pre-existing cells.”  THE CELL THEORY Three principles/components of cell theory All living organisms are composed of one or more cells. Cell is the basic structural and functional unit of living organisms. All cells arise from pre-existing cells.  EXAMPLES OF POSTULATE 1 UNICELLULAR ORGANISMS- singled-cell can perfom all the essential functions that enable it to grow, survive, and reproduce. MULTICELLULAR ORGANISMS- organisms are more complex in structure and functions, but the mechanisms on how they are able to live is still the same as with simple life forms.  UNICELLULAR ORGANISMS AMOEBA EUGLENA BACTERIA PARAMECIUM MULTICELLULAR ORGANISMS PLANT CELL ANIMAL FUNGI CELL  Early Forms of Life The first form of life is believed to have appeared some 3.5 billion years ago. The first evidence of life is found in microfossils.  Microfossils Microfossils are fossils that contain the remains of tiny plants and animals. Some of the remains of organisms do not have a nucleus so they were called prokaryotes. They are known to be the earliest forms of life. They have survived the extreme conditions of the early environment. They started to make their own food by utilizing the energy from the sun and the carbon dioxide in the atmosphere. These are the photosynthetic organisms. The process of photosynthesis produced more oxygen that changed the Earth’s early atmosphere. This change in the atmosphere allowed oxygen-breathing organisms to exist. Prokaryotes Prokaryotes are unicellular organisms that lack organelles or other internal membrane-bound structures. Most prokaryotes have a cell wall outside the plasma membrane and have double- stranded DNA located in an area of the cell called the nucleoid.  Eukaryotes Eukaryotes are organisms whose bodies are made up of eukaryotic cells, such as protists, fungi, plants and animals. Eukaryotic cells are cells that contain a nucleus and organelles, and are enclosed by a plasma membrane.  The cyanobacteria are the first photosynthetic organisms to form. Their microfossils are among the easiest to recognize. Their morphology remained the same and they left chemical fossils in the form of broken products from pigments. The first microfossil that showed remains of organisms with differences in structure from the simple form of life was seen in rocks about 1.5 billion years old. They are larger than bacteria and have internal membranes and thicker walls. These findings marked the beginning of eukaryotic organisms on Earth.  Theories about the Origin of Life PANSPERMIA Life did not begin on Earth at all but was brought here from elsewhere in space. Special Creation Theory States that life was created by a Supreme being called GOD.  Theories about the Origin of Life ABIOGENESIS Life evolved from inanimate objects. ❖Models of Abiogenesis ✓Spontaneous Generation ✓Primordial Soup Theory ✓The Clay Hypothesis ✓Deep Hot Biosphere Hypothesis  ❖Models of Abiogenesis Spontaneous Generation The formation of living organisms w/out arising from a similar organism. Example: OBSERVATION: Since there were no refrigerators, the mandatory, daily trip to the butcher shop, especially in summer, meant battling the flies around the carcasses. Typically, carcasses were “hung by their heels,” and customers selected which chunk the butcher would carve off for them. CONCLUSION: Obviously, the rotting meat that had been hanging in the sun all day was the source of the flies.  DISPROVING SPONTANEOUS GENERATION THEORY Francesco Redi ✓Italian Physician ✓Disapproved Spontaneous Generation Theory ✓His hypothesis was that rotten meat does not turn into flies. ✓Used open and closed flasks w/c contained meat.  REDI’S EXPERIMENT Evidence against spontaneous generation: 1. Unsealed- maggots on meat 2. Sealed- no maggots on meat 3. Gauze- few maggots on gauze, non on meat  DISPROVING SPONTANEOUS GENERATION THEORY Lazzaro Spallanzani ✓Italian Physiologist, Biologist, and Priest ✓Disapproved Spontaneous Generation Theory ✓Boiled soups for almost an hour and sealed containers by melting the slender necks. - The soup remained clear. - Later, he broke the seals and the soups become cloudy with microbes. SPALLANZANI’S EXPERIMENT  DISPROVING SPONTANEOUS GENERATION THEORY Louis Pasteur ✓French chemist and microbiologist ✓Disapproved Spontaneous Generation Theory ✓Used an S-Shape flask in disproving spontaneous generation theory. ✓His Hypothesis: Microbes come from cells of organisms on dust particles in the air; not the air itself.  ❖Models of Abiogenesis Primordial Soup Theory ✓It suggests that life began in an ocean or pond. ✓Proposed by Russian scientist Alexander Oparin. ✓Supported by the Miller-Urey experiment proposed by Stanley Miller and Harold Urey.  ❖Models of Abiogenesis The Clay Hypothesis It suggests that the first molecules of life might have met on clay, whose surfaces not only concentrated these organic compounds together, but also helped organize them into patterns. Deep Hot Biosphere Hypothesis It suggests that life did not begin on the surface of the Earth but instead in the porosity of its crust.  EVOLUTION OF LIFE THEORY OF ADAPTATION ✓Jean Baptiste de Lamarck French scientist ✓If an organism changes during life in order to adapt to its environment, those changes are passed on to its offspring.  EVOLUTION OF LIFE NATURAL SELECTION ✓Charles Darwin, English naturalist and geologist. ✓He published Origin of Species by Means of Natural Selection. ✓more individuals are produced each generation that can survive. Phenotypic variation exists among individuals and the variation is heritable. Those individuals with heritable traits better suited to the environment will survive.  MECHANISMS OF CHANGE 1. Mutation -Very occasionally, little copying or change (mutations) occurs during the process of DNA replication. 2. Gene flow -A result of migrating individuals that breed in a new location. 3. Recombination -Because of sexual reproduction, new gene combinations are introduced into a population; thus it can be an important source of genetic variation. 4. Genetic Drift -Any change in the allele frequencies in a population due to random sampling.  SELECTION IN HUMANS 1. Natural Selection- when the environment changes, natural selection often favors different traits in a species. Human are significantly changing the environment in number of ways; we therefore should not be surprised to see biological species that try to adapt to these new conditions. 2. Artificial Selection- it is sort of controlled by human purpose rather than natural forces. SELF-CHECK 1. What are the characteristic of life? 2.What are the Theories about the Origin of Life? 3. Who are the scientist that disprove spontaneous theory? 4.What is the difference between lamark and Darwin’s Theory of Evolution?