Growth Differences 28

Growth Differences : 

Growth Differences

Growth : 

Growth GROWTH is the irreversible increase in dry mass of an organism involving the increase in cell number and cell size. DRY MASS is used as fresh mass is unreliable due to the temporary fluctuations that can occur in an organisms water content. PERENNIAL PLANTS: are those that grow continuously year after year. ANNUAL PLANTS: are those that only live one growing season

Meristems : 

Meristems In plants growth occurs in regions called MERISTEMS. These are a group of undifferentiated plant cells that are capable of dividing repeatedly. PRIMARY growth occurs at APICAL meristems SECONDARY growth occurs at LATERAL meristems

Apical Meristems : 

Apical Meristems APICAL meristems occur at the root tip and shoot tip. These increase the length of the root and shoot by: mitosis and cell division. The cells become elongated, vacuolated and then differentiation. Increasing cell number Increased cell size Longitudinal cell division Nucleus disintegrates Lignin deposited on inside of cell wall End wall disintegrates leaving hollow tube for water transport. Xylem Nucleus disintegrates Sieve plate forms from cytoplasmic strand allowing translocation through sieve plate Phloem e.g. Growth in shoot

Lateral Meristems : 

Lateral Meristems As a perennial plant requires more xylem tissue to provide additional support and transport water . The development of the extra xylem each year makes a tree increase in thickness. The secondary xylem is produced by the cambium. Phloem Xylem Cambium Radial: A complete ring of Cambium is formed Tangential: Inside- secondary xylem (wood), large amounts Outside- secondary phloem, small amounts

Secondary Thickening : 

Secondary Thickening

Annual Rings : 

Annual Rings Different sizes of xylem vessel are formed at different times of the year Conditions Affecting Annual Rings Warm Weather Wet weather Cold conditions Dry conditions Leaf loss Wider Ring Narrower rings

Regeneration : 

Regeneration Flowering plant has an extensive ability to REGENERATE. The whole plant grows from small parts used in growing. Mammals have a limited ability to REGENERATE. Occurs in some tissues only, such as liver, and skin The more changed a cell is the more difficult regeneration is.

Growth Patterns in Plants & Animals : 

Growth Patterns in Plants & Animals Growth can be measured by increases in Size Dry mass Wet mass Typical ‘S’ growth curve Initial loss of mass during germination then loss of mass due to seed dispersal height Dry mass Annual Plant height Tree keeps growing for a long time Loss of mass due to leaf fall Perennial Plant

Regeneration : 

Regeneration REGENERATION is the process by which an organism replaces lost or damaged parts. Flowering Plants have extensive powers of regeneration. Commercially: cuttings are taken to increase the supply of a desirable plant. Mammals have limited regeneration power. It is restricted to the healing of wounds, the mending of bones, the replacement of blood, and regeneration of damaged liver.