Living vs. Non-Living Things: Understanding Life

Living and Non-Living Things

• Organisms can be unicellular or multicellular
• A living thing is defined as an organism that can carry out life processes

MRSGREN

• Movement - used to find food, mates, shelter or evade predators
• Respiration - (energy production)
• Sensitivity/Stimulus - (detecting and responding to changes)
• Growth - (the ability to make more cells)
• Reproduction - (the ability to pass on genetic info)
• Excretion - (remove wastes)
• Nutrition - (take in and use appropriate nutrients)

Movement

• External movement includes walking, running, swimming, flying, or sliding
• Internal movement involves materials moving around cells, tissues, organs, and organ systems
• Plants move in response to temperature, humidity, and sunlight, and their roots respond to water availability and nutrients
• Bacteria and fungi move to find food and water
• Certain bacteria species use flagella for liquid medium locomotion

Respiration

• Living things need a constant energy supply
• Respiration happens in both unicellular and multicellular organisms
• Carbohydrate molecules, like glucose, break down to release stored energy
• Cells capture energy and store it as adenosine triphosphate (ATP)
• Stored energy releases when ATP breaks down to power life processes
• Aerobic respiration is the full breakdown of glucose with oxygen
• Anaerobic respiration is partial glucose breakdown with limited or no oxygen

Sensitivity

• A stimulus causes a physiological response in an organism
• Common stimuli include changes in light, heat, sound, and chemical action
• Sharks,for example, detect electric currents from distressed animals kilometres away
• Tomatoes grow towards sunlight
• Unicellular organisms respond to small environmental changes by moving

Growth

• Growth and development come from cell division
• Cell division needs energy

Growth in Multicellular Organisms

• Growth involves increases in cell size and number
• Growth is essential for development and damaged tissue repair

Growth in Unicellular Organisms

• Growth is about increasing the number of cells in a population
• Growth is essential for continuation of the colony

Reproduction

• Living things reproduce sexually or asexually
• Asexual reproduction involves a single organism reproducing independently; offspring are genetically identical
• Sexual reproduction involves parent organisms producing specialized cells (gametes), forming a single cell that multiplies and develops, resulting in non-identical offspring

Excretion

• Excretion removes metabolic wastes from the body
• Toxic waste forms during respiration and cellular processes
• Unicellular organisms release waste directly via diffusion
• Multicellular organisms use specialized organs and systems
  • Plants excrete carbon dioxide (from respiration) and oxygen (from photosynthesis) through simple diffusion
  • Animals excrete carbon dioxide (respiration), water and salt (sweat), and urea (metabolism)
  • Kidneys, liver, lungs, and skin remove wastes from the human body

Nutrition

• Living things source, extract, process, and use nutrients and energy to power life
• Some nutrients build larger molecules in cells
• Animals get nutrients from plants and other animals

Plants

• Plants transform inorganic molecules into glucose during photosynthesis

What Is a Cell

• A cell is the smallest independent unit of life
• It has a highly organized structure for its function
• Living things are organisms
• All organisms have one or more cells

Cell Theory

• Describes properties of cells
• Originated in the 17th century from Hooke and Leeuwenhoek's observations
• The cell theory has three principles:
  • Cells are the smallest structural and functional unit of life
  • Cells originate from existing cells through cell division
  • Cells contain hereditary material (DNA)

Cells and Nucleus

• Prokaryotic cells dont have a defined nucleus (bacteria)
• Eukaryotic cells have a defined nucleus (all other cells, e.g., plant and animal cells)

Cell Structure

• All cells have a membrane enclosing the cell
• Cytoplasm within the cell is mainly water (cytosol) and organelles
• Organelle types depend on the cell type

Prokaryotic Cells

• Refers to cells "before nucleus"
• Prokaryotes are simple, single-celled organisms that lack a nucleus and membrane-bound organelles
• DNA is in the nucleoid region and is a single, large, circular chromosome
• Ribosomes are in the cell cytoplasm
• The rigid cell wall is made of peptidoglycan (sugar + protein), which provides protection, shape maintenance, and prevents dehydration
• Many bacteria have a sticky carbohydrate capsule for surface attachment

Eukaryotic Cells

• Refers to cells with a "true nucleus"
• The DNA is packaged into chromosomes in the nucleus
• Eukaryotic cells have membrane-bound organelles
• Respiration occurs in the cytoplasm and mitochondria
• Photosynthesis occurs in chloroplasts
• Plants have a cell wall for structural support and a vacuole for storing food, water, and waste

Prokaryotic vs Eukaryotic Cells

• Prokaryotic cells are smaller (1-10 µm) compared to eukaryotic cells (10-100 µm)
• Prokaryotic cell DNA is circular; Eukaryotic is linear
• Prokaryotes have a single chromosome; eukaryotes have multiple
• Prokaryotes lack membrane-bound organelles; eukaryotes contain them
• Prokaryotes have no nucleus, eukaryotes have one
• Most prokaryotes have a cell wall of peptidoglycan; some eukaryotes have a cell wall of cellulose

Nucleus

• Controls cell activity by determining which proteins to make via protein synthesis, which affects structure and function
• Stores genetic material (chromosomes) to coordinate internal cell processes
• Has a double membrane nuclear envelope with nuclear pores controlling entry and exit

Nucleolus

• Region within the cell nucleus
• Is responsible for producing and assembling ribosomes

Lysosome

• Organelles contain digestive enzymes
• Break down waste materials, like catalase breaking down toxic hydrogen peroxide into water and oxygen

Chloroplast

• Plastids in plants and algae are involved in food synthesis and storage, carrying out photosynthesis
• Double membrane-bound organelles with thylakoids (membrane-bound compartments)
• Large surface area maximizes photosynthetic pigment (chlorophyll) capture of light energy

Mitochondria

• Carry out the latest stages of respiration in plants and animals
• Cells like muscles and sperm require many mitochondria
• Have two membranes, the inner one folded into cristae for a large surface area, allowing for efficient synthesis of ATP for energy

Golgi Body

• Stacks of membrane sacs
• Involved in packaging and secreting proteins and lipids, especially those exported from the cell
• Substances are packaged into vesicles, which bud off, move to the cell membrane, fuse, and release contents (cytosis)

Endoplasmic Reticulum

• Tubule system from the nuclear envelope to the cell membrane
• Transports materials within the cell

Rough Endoplasmic Reticulum

• Has ribosomes attached to its surface
• Immediately adjacent to the cell nucleus
• It is involved in synthesis proteins and membranes

Smooth Endoplasmic Reticulum

• Involved in synthesizing lipids and carbohydrates.

Ribosome

• Cellular particle made of RNA and protein
• Site for protein synthesis
• Reads messenger RNA (mRNA) sequence and translates RNA bases into amino acids using the genetic code

Vacuole

• Fluid-filled spaces contained by a membrane that can contain solutes like salts, sugar and amino acids
• They are used in the control of water and salt balance
• In animal cells, vacuoles help sequester waste products
• In plant cells, vacuoles help maintain water balance and cell shape

Centriole

• Barrel shaped organelle within the centrosome
• The centrosome is the area of cytoplasm next to the nucleus
• Centrioles are made up of microtubules
• They are essential for cell division

Cytoskeleton

• Made of proteins
• Maintains cell shape and internal organization
• Provides mechanical support to carry out division and movement

Cell Division

• Makes new cells for growth and repair
• Cells divide from pre-existing cells
• Process varies between prokaryotic and eukaryotic cells
• All cells work due to their genetic code (DNA)
• Deoxyribonucleic acid (DNA) is a set of instructions found on chromosomes, called genes

Humans

• Humans have 46 chromosomes (diploid 2n=46)
  • Each one has a set of genes (height, nose shape, hair colour etc)
• In cell division, one cell (parent cell) divides into two (daughter cells)
• Before dividing, a cell replicates its DNA, giving each daughter cell an identical copy of instructions
• Semi-conservative DNA replication results in each new DNA molecule containing one strand from the parental molecule and a newly synthesized strand
• Strands of parental molecules separate, each acts as a template for synthesising a complementary strand

Prokaryotic Cell Division (Binary Fission)

• Prokaryotes reproduce asexually through binary fission
• Parent cell divides into two equal and identical daughter cells, taking 15 minutes to hours
  • Chromosomes are replicated producing identical copies
  • Each chromosome is attached by proteins to the cell membrane
  • A new wall forms forming two daughter cells.

Genetic Variation In Prokaryotes

- Mutation is a base change (deletion, insertion or substitution) in DNA
- Conjugation involves plasmids (DNA) being transferred between bacteria

Eukaryotic Cell Division (Mitosis)

• Mitosis Eukaryotic division is more complex than binary fission
• Cell are diploid (2n) = 2 sets of chromosomes
• In humans=46 chromosomes in the cell nucleus:
  • 23 chromosomes from mum
  • 23 chromosomes from dad
• Chromosomes consist of chromatin (DNA + Protein called histones)

Interphase (Before Mitosis) (SEMI-conservative)

• DNA replicates before mitosis
• Is created a chromosome of two sister chromatids joined by a centromere
• After, chromatin condenses into a visible chromosome
• Unduplicated chromosomes are single stranded
• Replicated chromosomes are double stranded
• Inter phase consists of three steps:
  • G Phase: grows larger, and organelles are copied (10 hours)
  • S Phase: synthesizes a copy of the DNA (5 to 6 hours)
  • G Phase: grows more, makes protein and organizes contents (3 to 4 hours)
• Cells that divide slowly may exit the G phase for a non-dividing state (GO)

Mitosis - Prophase

• Chromosomes condense and become visible under a microscope
• Nuclear membrane disintegrates
• Centrioles move towards the poles (opposite ends of the cell).
  • Note: plants don't have centrioles
• Centrioles' (made of protein) produce spindle fibres
• Spindle fibres attach to the chromosomes at their centromere

Mitosis - Metaphase

• Chromosomes fully condensed
• Attached to the spindle fibres at the centromere, line up the equator (metaphase plate) of the cell

Mitosis - Anaphase

• Spindle fibres contract, pulling centromeres on sister chromatids towards opposite poles
• Cells begin to elongate

Mitosis - Telophase

• Chromosomes reach the poles
• Spindle fibres disassemble
• New nuclear membranes are synthesized around each set of chromosomes
• Chromosomes revert back to chromatin (less condensed) Cytokinesis
• After mitosis, the cell completes cell division by splitting
• An indentation (cleavage furrow) forms in animal cells
• It divides the cytoplasm
• The cleavage furrow contracts until the parent cell is cleaved into two daughter cells

Final Note

• Each daughter cell is genetically identical to each other and to the original parent cell

Cells Require Energy

• The source(s) of energy are light (most autotrophs) and chemical (heterotrophs)
• Photosynthesis, respiration, and fermentation are important energy processes for cells
• Cells require materials and the removal of wastes
• Cells require energy to function
  • All living things use energy for movement, synthesis and maintenance of a stable intracellular environment (homeostasis)
• Law of Conservation of Energy: energy cannot be created or destroyed, energy can be simply changed from one to another - Forms of energy: light and chemical
• Chemical reactions occur continuously in cells
  • Metabolism is the term used to described all the chemical reactions that occurs in cells
• Chemical energy is energy stored in the bonds of atoms and molecules
  • All metabolic reactions involve changes in energy

Catabolic Reactions

• Break large molecules into smaller molecules
• Releases energy

Anabolic Reactions

• Synthesize larger molecules from smaller molecules
• Requires energy

Energy Release and Capture

• For catabolic reactions a molecule called Adenosine triphosphate (ATP), stores the energy to be used in anabolic reactions
• The energy is used to attach an inorganic phosphate group on to ADP (Adenosine diphosphate)
• The energy is stored in the bonds between the phosphate groups

ATP Cycle

• Energy trapped in ATP is released by breaking the weak bond connecting the last phosphate group and then can be used in anabolic reactions
• The cycle then continues
• ATP is continually being synthesised and broken down in the body which then provides an organism with energy
• ATP is synthesised during photosynthesis, respiration and fermentation

Heterotrophs

• Heterotrophs obtain food and energy by consuming other organisms

Autotrophs

• Autotrophs produce energy-rich molecules (Light energy is converted into chemical energy)

Photosynthesis

• Plants use light energy, carbon dioxide from air, and water from soil to create glucose
• Oxygen is also a by-product
• Excess glucose stores as starch (polysaccharide)
• Photosynthesis is an anabolic process (synthesis reaction) that occurs in the cells of photoautrophs
• Plant cells contain organelles called chloroplasts, which use a green pigment called chlorophyll that absorbs light

Cellular Respiration

• Cellular respiration is the process of extracting energy from complex molecules (glucose) and generate ATP

Respiration (Catabolic Process)

• A catabolic process (break down reaction)
• Occurs in autotrophs and heterotrophs
• There are two types of respiration
  • Aerobic releases energy from breaking down glucose with oxygen
  • Fermentation - anaerobic breaks down glucose without oxygen
• Aerobic respiration produces ATP by breaking down glucose entirely with oxygen
• Aerobic respiration creates water and carbon dioxide
• Aerobic respiration produces 36 ATP molecules

Fermentation - Alcohol

• In yeast results in alcohol, carbon dioxide and 2 ATP molecules
• The incomplete breakdown of glucose leads to carbon dioxide and ethanol

Fermantation - Lactic Acid

• Lactic creates lactic acid
• Takes place in animal cells and certain bacteria which dont have enough oxygen

Waste Type by Respiration Types

• The blood transports carbon dioxide to the lungs, and the body exhales it
• The body excretes water through urine, sweat, or vaporized breath
• CO₂ enters the environment, ethanol flows out of the cells and accumulates in the medium
• The bloodstream transports lactic acid to the liver for conversion back to pyruvate, some excreted through sweat or urine

Movement Across the Cell Membrane

• A cell membrane regulates the movement of substances into and out of the cell
• Selectively permeable, permeable to some and selective to others
• Permeability depends on substance size and charge

Molecule Movement

• Small, hydrophobic molecules like oxygen and carbon dioxide diffuse through the lipid layer without energy (passive movement)
• Water requires aquaporin proteins in the cell membrane to move rapidly

Transport Factors

• Concentration gradient
• Thickness and surface area of the membrane
• Temperature
• Availability of membrane proteins