“All living things grow and develop” Cell Growth “All living things grow and develop”

Cell Size Limitations Over burdened DNA Surface area to volume ratio DNA = nucleic acid that provides instructions to ribosomes to produce protein DNA controls activities of the cell within the nucleus Surface area to volume ratio Surface area increases slowly Volume increases quickly Just can’t get enough or get rid of enough Cell membrane is site of material exchange Diffusion, facilitated diffusion, osmosis too slow

DNA Overload There’s too much work!!! Not enough information to go around in the cell As a cell grows, it has more organelles and conducts more activities Cellular activities require enzymes Enzymes are proteins; therefore, must be produced through protein synthesis Protein synthesis requires information from DNA

Just Can’t Get Enough Can’t get enough oxygen, food and water across the cell membrane to supply the cell Can’t get rid of waste products quickly enough to prevent self poisoning Process of diffusion/osmosis is too slow

Surface Area to Volume Ratio The surface area increases slower than the volume . . . OR . . . The volume increases faster than the surface area!! Therefore, the surface area to volume ratio decreases!! More volume = more demands because the rate of consumption increases Surface area can’t keep up with demands

Surface Area

Surface Area vs. Volume Surface area = 96 mm2 Volume = 64 mm3 Surface area to volume ratio: 6:1 or 6/1 = 6 Surface area to volume ratio: 24:8 or 24/8 = 3 Surface area to volume ratio: 96:64 or 96/64 = 1.5 As a cell grows, notice the value of the surface area to volume ratio! It decreases!

So . . . What can cells do about that? Cell division – the process used by cells to divide Dividing rectifies the problem of putting too much demand on DNA Dividing increases the surface area to volume ratio Dividing reduces the size of the cell making it possible to distribute nutrients and remove waste!

Replication DNA makes copies of itself Review: DNA unzips Complementary nucleotides attach Two new strands of identical DNA are produced Each new strand has one strand from the original DNA must be copied so that each new cell has a complete set of DNA of the original

Reproduction Reproduction is the production of offspring or a new organism There are two general methods/strategies of reproduction: Asexual reproduction – production of offspring that requires only one parent Sexual reproduction – production of offspring that requires the combination of two different cells

Asexual Reproduction Organisms produce offspring through one parent Offspring have the same genetic information (information for making proteins) as the parent They are, in essence, clones!!! Unicellular organisms, like bacteria, usually reproduce asexually Some multicellular organisms reproduce asexually

Asexual Reproduction & Multicellular Organisms Organisms such as plants and protists can reproduce asexually Hydra reproduce through budding! Plants can reproduce asexually Bulbs Cuttings Rhizomes Roots/shoots/runners

Budding in Hydra

Binary Fission of Amoeba

Runners of Strawberry Plants

Asexual Reproduction in Plants

Asexual Reproduction = Clones

Sexual Reproduction Sexual reproduction is a process where two cells (gametes) from different parents join together to form a new organism Offspring of sexual reproduction have different genetic information from both parents Most plants and animals and some unicellular organisms reproduce sexually

Sexual Reproduction

Asexual vs. Sexual Reproduction No need to find mate; therefore, quicker No genetic diversity; therefore, vulnerable Sexual Must find a mate; therefore, slower Genetically diverse; therefore, healthy