Characterists of Life

Characteristics of Life

Living Things

Are highly organized and contain complex substances

Are made up of one of more cells

Use energy

Have a form and a limited size

Have a limited life span

Grow

Respond to changes in the environment

Reproduce

Evolve and change over time

Life Process Needed to Sustain Life

Nutrition

Taking the nutrients from the environment (ingestion-heterotrophs)

Breakdown of complex foods into simpler ones (digestion)

Egestion (elimination

Autotrophs (produce own food)

2) Transport

Substances distributed throughout the organism

Plants (conducting tissues)

Animals (circulatory system)

3) Respiration - Cellular

release of stored engery in nutrients

occurs within the cells

Meiosis

Intro

The division of sex cells (germ cells) at maturation (for woman it is during ovulation, for men it is always)

Also known as gametes —> egg and sperm

They contain half the genetic information (human gametes contain 23 chromosomes each, one of each pair of chromosomes)

Ensures genetic variability (no two organisms are generically alike)

Haploid: one copy of each type of chromosome (n) — in humans n=23

Diploid: two copies of each type of chromosome (2n) - in humans 2n=46

Homologous chromosome: are a pair of chromosomes that contain the same genetic information

Tetrads: refers to the four sister chromatids (two from each chromosome) in a homologous pair

Stages of Meiosis

MEIOSIS I

Prophase I

DNA replicates (late interphase)

Nuclear membrane dissolves

Centrioles move to opposite poles

Spindle fibres are formed

Homologous chromosomes pair up forming a tetrad (synapsis)

During this time crossing over may occur: Homologous chromosomes may intertwine chromatids and then break and exchange information (the exchange occurs in anaphase)

Metaphase I

Homologous chromosomes line up at the equatorial plate and attach to the spindle fibres

Anaphase I

Homologous chromosomes