CHAPTER 5

Earth is said to be a little over 4.5 billion years old.

The oldest material found on earth that is estimated to be 4.3 billion years old is a ZIRCON CRYSTAL

Continents were not yet present only a huge ocean with scattered small islands.

About 3.8 BILLION YEARS AGO, life on earth initially began with single celled PROKARYOTIC CELLS

Over a billion years later multicellular life evolved.

life forms began to evolve 570 MILLION YEARS AGO(MYA)

• started early with arthropods

• followed by the fish (530 MYA)

• land and plants and forests (475 and 385 MYA)

• mammals emerged around (200 MYA)

• homo sapiens evolved 200,000 years ago.

The CELL is the BASIC UNIT OF LIFE.

All CELLS come from PRE EXISTING CELLS.

CREATION THEORY

-The concept of divine creation is that all life forms existing today on earth have been created by a supreme being.

-In Hinduism , it is believed that BRAHMA , the God of creation created the living the world.

-Christians , Jewish , and Islamic beliefs state that God created the universe , plants, animals , and humans in six days.

-Most creationists believe that the current form of species is the same as the original form that God created.

THEORY OF ABIOGENESIS

-Theory of Abiogenesis or the Spontaneous Generation theory that living things were naturally created from non living things.

-Abiogenesis occured between 3.8 and 4 BYA (BILLION YEARS AGO)

-The experiment performed by STANLEY MILLER in 1953 gave way many speculations and studies on how life on earth really began.

-He demonstrated how an electric spark (which is a simulation for lightning) when passed through simple organic gases (similar to the early atmosphere of Earth), resulted in the formation of amino acids, which are now known as the building blocks of proteins and the components of living tissues.

THEORY OF BIOGENESIS

-presented a strong argument against abiogenesis.

-this theory states that living things come from living things.

-Experiments of FRANCESO REDI and LOUIS PASTEUR disproved the thought of spontaneous generation.

• Francesco Redi is a physician, a naturalist, and a poet.

• Louis Pasteur is a French chemist and microbiologist.

• The idea of spontaneous generation was popular until almost the seventeenth century. Even the likes of Descartes, Galileo, and Helmont, famous scientists of that period, believed in this theory.

THEORY OF CATASTROPHISM

• supported by french scientists Georges Cuvier and Orbigny.

• it states that there have been several living creations from God each encountered a catastrophe. which completely destroyed them

• each new creation consisted of new life forms and they happen to be different from the previous ones.

CHARACTERISTICS OF LIVING THINGS

• All living things are made up of cells

• Cells are the basic building blocks of all living things.

• Each sell contains materials that carry out basic life processes like respiration.

• Single celled or unicellular organisms include the bacteria , some protists and some fungi.

Multicellular organisms - they are composed of many cells, which are grouped together and perform specific tasks in the body.

Two kinds of organisms according to their cell structure; prokaryotes and eukaryotes

Examples of multicellular are animals and plants.

• Prokaryotes are single-celled organisms that lack a membrane-bound nucleus, mitochondria, and all other organelles. Its name comes from the Greek words pro, which means "before,, and karyon, which means "nut or kernel."

• Eukaryotes are organisms with cells that contain membrane-bound nucleus and other membrane-bound organelles.

  -The nucleus of a eukaryotic cell contains the genetic material (DNA), enclosed by a nuclear envelope. Other membrane-bound organelles are mitochondria, Golgi apparatus, and chloroplast found in photosynthetic organisms such as algae and plants.

  -There are also unicellular eukaryotes known as protozoa. All other eukaryotes are multicellular organisms such as plants, animals, and fungi.

3 tenets of cell theory:

1.) living things are composed of one or more cells.

2.) The cell is the basic unit of life.

3.) All cells arise from preexisting cells.

The discovery of the cell is largely attributed to Robert Hooke. Upon examining a piece of cork using a microscope that he built, Hooke observed tiny compartments which he called "cells" (Latin: little room).

Matthias Schleiden suggested that all structural parts of plants are made up of cells. In 1839, Theodore Schwann stated that along with plants, all animals are composed of cells. From these conclusions about plants and animals, advancement on the study of animal parts and functions began. In 1855, Rudolf Virchow included the idea that all cells come from preexisting cells.

LIVING THINGS METABOLIZE

Chemical reactions:

Building up = Anabolism

Breaking down = Catabolism

In anabolism, the substances needed by organisms to grow, store energy, and repair tissues are synthesized.

This chemical building up and breaking down processes are collectively called metabolism. Metabolism, from the Greek word metabole, which means "change," is the sum total of all the life-sustaining chemical reactions in living things. It allows living things to grow, maintain their structures and functions, and respond to stimuli.

LIVING THINGS GROW AND DEVELOP

• In all living things, growth involves the increase in one’s size or height.

• However, grow is not just an increase in physical structure.

• It also involves complex changes in an organism.

MICROORGANISMS such as bacteria also undergo growth and development, reach maximum size and maturity.

• a LIFE SPAN is the maximum length of time a living thing can live.

• humans have average life expectancy of 60 to 70 years

• Some plants, such as narra trees, can live for more than 100 years.

LIVING THINGS RESPOND TO STIMULI

-All living things respond to stimuli in the environment.

-This responsiveness makes them survive. Stimulus (plural: stimuli) is any signal or change in the environment of an organism that produces a response or reaction from that organism.

-Responses to stimuli depend on the need of an organism.

-Homeostasis is the internal balance of the body or system of living organisms. This balance is needed for the proper function and regulation of the living thing's body.

LIVING THINGS INTERACT

No living organism can live alone and interactions amongst organism is simultaneously happening on earth.

Eco system - is formed when a community of organism interact with other community and with their environment.

interactions that happen among organisms, mainly:

• Feeding relationships

• Life cycle of organism

• Exchange of gases in plants and animals

LIVING THINGS REPRODUCE

• The ability of living things to produce offspring of its own kind is called reproduction.

• Reproduction is not an individual organism's need, rather, it is for the species' need for perpetuation.

• Many organisms become extinct because they are unable to reproduce their own kind.

• Sexual reproduction involves the union of sex cells or gametes-the egg cell from a female organism and sperm from a male organism.

• Other simple organisms, such as bacteria and plants, can reproduce asexually.

In both cases the generic material DNA is passed on from one generation to the next, ensuring the survival of the species on earth.

LIVING THINGS ADAPT AND EVOLVE

-All living things can adapt to their environment. This adaptation is necessary for survival.

-Prolonged adaptation to certain environments may lead to the gradual evolution of succeding generations.

• Adaptation - is any response to reaction towards a stimulus that helps in the survival of an organism.

• Evolution - is the gradual change in organisms over a period of the in response to changing environment.

LIVING THINGS ARE ORGANIZED

• Atom - Is the smallest amount of matter.

• Molecules - Are combinations of atoms.

• Cell - Is the basic unit of life.

• In multicellular organisms like plants and animals, cells are grouped as tissues to perform specific functions. Different tissues can be grouped together and form organs.

CHAPTER 6

BIOENERGETICS

Energy is the ability to do work.

All life forms need energy.

Food consists of organic molecules that store energy in the form of chemical energy.

• AUTOTROPHS - An organism that can produce its own food using light, water, carbon dioxide, or other chemicals.

  -they are aslo called producers.

  -most of them use energy from sunlight.

• HETEROTROPH - organisms that cannot make their own food obtain food by consuming other organisms.

  -heterotrophs include animals , fungi ,and some single celled organisms.

• Glucose is made during the process of photosynthesis.

With the help of light energy from the sun, water, and carbon dioxide, plants create glucose, where chemical energy is stored in a concentrated and stable form. In the human body, glucose is transported by the blood and taken up by the cells for energy source.

The stored energy in glucose is released in a reverse reaction of photosynthesis called cellular respiration.

• Adenosine triphosphate (ATP) molecules store smaller amount of energy, but each molecule releases enough energy to do the work within the cell.

It is the energy-carrying molecule used by the cell. ATP is made during the first half of photosynthesis and is used during the second half where glucose is made. It is also used for energy by the cells for other important cellular processes.

PHOTOSYNTHETIC ORGANELLES

Photosynthetic pigments are unique pigments found in all photosynthetic organisms such as plants and some bacteria.

Plants have two groups of pigments-chlorophylls and carotenoids.

• Chlorophyll a and chlorophyll b are green pigments that absorb all wavelengths of light in the red, blue, and violet ranges.

• Carotenoids are yellow, orange, and red pigments. They absorb light in blue, green, and violet ranges.

• The pigment found in red algae, called the phycobilins, which give them their reddish color, absorb light in blue and green ranges.

• Chloroplasts are cell organelles found in plants and algae.

  -produce energy through photosynthesis and oxygen release processes , which sustain plant growth and crop yield.

• each granum is made up of layers of sac like membranes called the THYLAKOIDS.

• PHOTOSYSTEMS are groups of molecules involved in photosynthesis.

  • functional units for photosynthesis.

  • two types are

  • PHOTOSYSTEM I (PSI)

    -absorbs light best in 680 nm range

  • PHOTOSYSTEM II (PSII)

    -absorbs light best in 700 nm range.

• the STROMA is the space found outside the thylakoids where the calvin cycle takes place.

• photosynthesis is often regarded as the most important life process on earth.

STAGE I : LIGHT DEPENDENT REACTIONS

-Light reactions take place in the thylakoid of the chloroplast.

-units of light called photons strike a molecule of chlorophyll in PS II.

-the light is absorbed by two electrons in the chlorophyll a which gives them enough energy to leave the molecule.

-the electron transport chain consist of plastoquinone , a complex of two cytochromes and other proteins.

-Nicotinamide adenine dinucleotide phosphate (NADP) an energy carrying enzyme becomes reduced when it picks up the two hydrogen ions from water in PS II.

STAGE II : LIGHT INDEPENDENT REACTIONS

-the second stage of photosynthesis happens in the stroma surrounding the thylakoids in the chloroplast.

-the reaction in this stage occur without the direct use of energy from light hence they are often called dark reactions.

• the discovery of this reaction by scientist MELVIN CALVIN won him a nobel prize in 1961.

• the light independent reactions are collectively called Calvin cycle or dark reactions.

Calvin has three major steps

• Carbon fixation - Carbon fixation occurs when carbon dioxide (CO,) from the atmosphere combines with a simple five-carbon (5-C) sugar compound, ribulose biphosphate (RuBP), forming an unstable six-carbon (6-C) molecule. The 6-C molecule is immediately broken down into two three-carbon (3-C) sugar phosphate known as 3-phophoglycerate (3- PGA).

• Reduction reactions - The 3-PGA molecules gain energy from the ATP and NADPH from the light reactions, and rearrange themselves to form glycerate 3-phosphate (G3P). This molecule also contains three carbon atoms but is more stable than 3-PGA. A single G3P molecule goes on to form into glyceraldehyde 3-phosphate, the three-carbon (3-C) carbohydrate precursor of glucose and other sugars. The rest of the G3P proceed to regeneration step.

• Regeneration of RuBP - The remaining G3P molecules then use more ATP to convert back into RuBP, completing the cycle. Converting the G3P molecules to the RuBP allows the cycle to repeat.