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

• 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: • 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:– 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