Transcript Cells: Agriculture`s Building Blocks

Cells: Agriculture’s Building
Blocks
Original Power Point Created by:
Andy Harrison
Modified by GA Agriculture Education Curriculum Office
July 2002
Cells
• All living organisms are composed of cells.
• The ability to study cells was first made possible
by the invention of the microscope.
• An understanding of cells has allowed scientists to
develop new products and technology.
• Some animals are only single cell organisms, such
as the amoeba, paramecia, and protozoa.
Cells
• One-celled bacteria are important for cattle health
and maintenance (ruminant digestion).
• Other bacteria are important for converting
atmospheric nitrogen to nitrogen for plant use.
• In addition, some cells such as the one-celled
phytoplankton are food for fish and whales.
Cell Characteristics
• Animals and plants contain specialized
cells, which vary in size and shape
– Largest – ostrich egg
– Smallest – bacteria
• Cell shape can be round, boxed, long, or
string-like.
• Other cells, such as amoebas, have the
ability to change shape constantly.
Reproductive Cells
• Reproduction begins in the cells.
• Male & female reproductive organs produce
cells that unite to form new organisms.
• All eggs are single cells.
Cell Structure – Cell Wall
• Plants have a cell wall, animals do not.
• Cell wall provides cell shape and protects
its contents
• The cell wall is composed of cellulose
which:
– Makes cell walls rigid
– Provides support for plant
– Used to make paper
Cell Structure- Cell Membrane
• Located inside the cell wall
• Also known as the plasma membrane
• All material going in and out of the cell
must pass through this membrane
• Membrance is semi-permeable; allows
certain substances (small molecules and
ions [charged molecules]) to pass through
Cell Structures- Cell Membrane
• Allows water and nutrients into and out of
the cell
• Transports waste out of the cell
• Membrane does this by a process called
diffusion.
– Diffusion: molecules pass through the
membrane from a region of higher
concentration to a region of lower concentration
Cell Structure- Cell Membrane
• Osmosis is the process where water passes
through a cell’s semi-permeable membrane from a
higher concentration to a lower concentration
– The less substance water has in it , the less concentrated
– The more substance – more concentrated
• Cells draw water inside their membranes to
equalize the concentrations on each side of the
membrane.
Cell Structure- Cell Membrane
• Homeostasis: the ability of an organism to
remain stable when conditions around it
change
• Turgid: cells filled with water so that they
are taut (firm)
• Turgor pressure: helps cells to retain their
shape
Cell Structure- Nucleus
• A relatively large structure
– Eukaryotic cells – have nucleus
– Prokaryotic – no true nucleus
• The nucleus is made of:
– Nucleic acids
– Proteins
– Enzymes
Cell Structure- Nucleus
• Surrounded by a double-layer membrane
– This membrane regulates movement of materials in and
out of nucleus, just as the cell membrane regulated
movement in and out of the cell itself.
• Contains genetic code
– Code is located in DNA (Deoxyribonucleic acid)
– DNA arranged in threadlike strands called
chromosomes
– Genes: segments of the chromosome; site of the actual
traits
Cell Structure- Cytoplasm
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Thick clear fluid surrounding nucleus
Constantly moving
Suspends other parts of cell
Contains all essential materials for cell life
process
Cell Structure- Organelles
• Small structures located in cytoplasm
– Mitochondria: peanut shaped; break down food
and supply cell with energy
• Cells requiring more energy (muscles) have a
greater number of mitochondria
– Vacuoles: storage compartments
• Membrane that encloses water and other material
• Stores cell waste
Cell Structure- Organelles
– Microtubules:
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Thin hollow tubes
Composed of protein
Function as the “bones” of the cell
In animals, they aid in chromosome movement
during cell division.
Cell Structure- Organelles
– Microfilaments: fine fiber-like structures made
of proteins
• Help the cell to move by oscillating back & forth
– Ribosomes: organelle where protein molecules
are assembled
– Enzymes: not an organelle, but important
compounds composed of proteins that regulate
chemical processes in cell
Cell Structure- Organelles
• Golgi apparatus: shaped like group of sacks
bundled together.
– Remove water from proteins and prepare it for
transport
• Lysosomes: digestive units of cells
– Digest proteins, carbohydrates, and other
molecules, including bacteria and worn out cell
parts
Cell Structure- Organelles
• Plastids: present in plants but NOT in
animals
• Three types:
– Chloroplast: contains chlorophyll, converts
sunlight energy to carbohydrates.
– Leucoplast: provides storage for cells
– Chromoplast: manufactures pigments that give
fruits and leaves color
Cell Reproduction
• All growth comes from cells increasing in
number
• When a cell reaches its maximum size, the
cell divides to increase in number.
• Original cell: parent cell
• New cells: daughter cells
Mitosis
• Process where the genetic code is
duplicated and passed on to daughter cells.
• The process is divided into phases:
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Interphase
Prophase
Metaphase
Anaphase
Telophase
Interphase
• Phase where cells are not actively dividing
• Not actually part of mitosis
• Cell begins to synthesize materials and
transport them outside of the cell
• Cell grows and reaches maximum size
• DNA replicates and forms two sets of
chromosomes
Prophase
• First actual phase of mitosis
• Chromatin appears in the form of distinct shorten
rod-like structures
– Chromatin is two strands called chromatids that are
attached in middle by a centromere
• Nuclear membrane begins to dissolve
• Nucleus begins to disperse
• In place of nucleus , a spindle is formed,
– A spindle is football shaped and made of microtubules
Metaphase
• Chromatids move toward center of spindle
• When they reach the center, they connect
themselves to the fibers of the spindle
Anaphase
• Pairs of chromatids separate into an equal
number of chromatids
• Centromeres duplicate
• Chromosomes move to opposite end of cell
Telophase
• Chromosomes continue to migrate to the
ends of the cell
• Remains of the spindle disappear
• New membranes are formed around the
chromosomes
– This forms two new nuclei
Cytokinesis
• Divides the cytoplasm in cell
• Separate process from mitosis
• In animals, the separation point is the
cleavage furrow in the center of the cell
• In plants, they form a cell plate and grow
outward until cells are separate