A growth curve is an empirical model of the evolution of a quantity over time. Growth curves are widely used in

biology Biology is the scientific study of life. It is a natural science with a broad scope but has several unifying themes that tie it together as a single, coherent field. For instance, all organisms are made up of cells that process hereditary i ...

for quantities such as

population Population typically refers to the number of people in a single area, whether it be a city or town, region, country, continent, or the world. Governments typically quantify the size of the resident population within their jurisdiction using a ...

size or biomass (in

population ecology Population ecology is a sub-field of ecology that deals with the dynamics of species populations and how these populations interact with the environment, such as birth and death rates, and by immigration and emigration. The discipline is import ...

and

demography Demography () is the statistical study of populations, especially human beings. Demographic analysis examines and measures the dimensions and dynamics of populations; it can cover whole societies or groups defined by criteria such as edu ...

, for population growth analysis), individual body height or biomass (in

physiology Physiology (; ) is the scientific study of functions and mechanisms in a living system. As a sub-discipline of biology, physiology focuses on how organisms, organ systems, individual organs, cells, and biomolecules carry out the chemical ...

, for growth analysis of individuals). Values for the measured property can be plotted on a

graph Graph may refer to: Mathematics *Graph (discrete mathematics), a structure made of vertices and edges **Graph theory, the study of such graphs and their properties *Graph (topology), a topological space resembling a graph in the sense of discre ...

as a

function Function or functionality may refer to: Computing * Function key, a type of key on computer keyboards * Function model, a structured representation of processes in a system * Function object or functor or functionoid, a concept of object-oriente ...

of time; see Figure 1 for an example...

Bacterial growth

In this example (Figure 1, see

Lac operon The ''lactose'' operon (''lac'' operon) is an operon required for the transport and metabolism of lactose in ''E. coli'' and many other enteric bacteria. Although glucose is the preferred carbon source for most bacteria, the ''lac'' operon allow ...

for details) the number of

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typically a few micrometr ...

present in a nutrient-containing broth was measured during the course of an 8-hour cell growth

experiment An experiment is a procedure carried out to support or refute a hypothesis, or determine the efficacy or likelihood of something previously untried. Experiments provide insight into Causality, cause-and-effect by demonstrating what outcome oc ...

. The observed pattern of bacterial growth is bi-phasic because two different sugars were present, glucose and lactose. The bacteria prefer to consume glucose (Phase I) and only use the lactose (Phase II) after the glucose has been depleted. Analysis of the molecular basis for this bi-phasic growth curve led to the discovery of the basic mechanisms that control gene expression.

Cancer cell growth

Cancer Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumors, which do not spread. Possible signs and symptoms include a lump, abnormal b ...

research is an area of biology where growth curve analysis plays an important role. In many types of cancer, the rate at which

tumor A neoplasm () is a type of abnormal and excessive growth of tissue. The process that occurs to form or produce a neoplasm is called neoplasia. The growth of a neoplasm is uncoordinated with that of the normal surrounding tissue, and persists ...

s shrink following

chemotherapy Chemotherapy (often abbreviated to chemo and sometimes CTX or CTx) is a type of cancer treatment that uses one or more anti-cancer drugs ( chemotherapeutic agents or alkylating agents) as part of a standardized chemotherapy regimen. Chemothe ...

is related to the rate of tumor growth before treatment. Tumors that grow rapidly are generally more sensitive to the toxic effects that conventional anticancer drugs have on the cancer

cell Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Locations * Monastic cell, a small room, hut, or cave in which a religious recluse lives, alternatively the small precursor of a monastery ...

s. Many conventional anticancer drugs (for example,

5-Fluorouracil Fluorouracil (5-FU), sold under the brand name Adrucil among others, is a cytotoxic chemotherapy medication used to treat cancer. By intravenous injection it is used for treatment of colorectal cancer, oesophageal cancer, stomach cancer, pan ...

) interfere with

DNA replication In molecular biology, DNA replication is the biological process of producing two identical replicas of DNA from one original DNA molecule. DNA replication occurs in all living organisms acting as the most essential part for biological inheritanc ...

and can cause the death of cells that attempt to replicate their DNA and divide. A rapidly growing tumor will have more actively dividing cells and more cell death upon exposure to such anticancer drugs. In the example shown in Figure 2, a tumor is found after the cell growth rate has slowed. Most of the cancer cells are removed by surgery. The remaining cancer cells begin to proliferate rapidly and cancer chemotherapy is started. Many tumor cells are killed by the chemotherapy, but eventually some cancer cells that are resistant to the chemotherapy drug begin to grow rapidly. The chemotherapy is no longer useful and is discontinued.

The growth of children

Children who fall significantly below the normal range of growth curves for body height can be tested for

growth hormone deficiency Growth hormone deficiency (GHD), or human growth hormone deficiency, is a medical condition resulting from not enough growth hormone (GH). Generally the most noticeable symptom is that an individual attains a short height. Newborns may also prese ...

and might be treatable with hormone injections. Image:Female Stature vs Age.svg, Female Stature vs Age (US CDC) Image:Male Stature vs Age.svg, Male Stature vs Age (US CDC)

Exponential growth

Some growth curves for certain biological systems display periods of

exponential growth Exponential growth is a process that increases quantity over time. It occurs when the instantaneous rate of change (that is, the derivative) of a quantity with respect to time is proportional to the quantity itself. Described as a function, a ...

. Typically, periods of exponential growth are of limited duration due to depletion of some rate-limiting resource.

Notes

Bibliography

External links

CDC recommended growth charts
{{DEFAULTSORT:Growth curve Population Population ecology Bacteriology Growth curves ja:増殖曲線